++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ The Boost Parameter Library Reference Documentation ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

:Authors: David Abrahams, Daniel Wallin :Contact: [email protected], [email protected] :organization: BoostPro Computing_ :date: $Date: 2005/07/17 19:53:01 $

:copyright: Copyright David Abrahams, Daniel Wallin 2005-2009. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

|(logo)|__

.. |(logo)| image:: ../../../../boost.png :alt: Boost

__ ../../../../index.htm

.. _BoostPro Computing: http://www.boostpro.com

//////////////////////////////////////////////////////////////////////////////

.. contents:: :depth: 2

//////////////////////////////////////////////////////////////////////////////

.. role:: class :class: class

.. role:: concept :class: concept

.. role:: function :class: function

.. role:: vellipsis :class: vellipsis

.. section-numbering:: :depth: 2

Preliminaries

This section covers some basic information you'll need to know in order to understand this reference.

Namespaces

In this document, all unqualified identifiers should be assumed to be defined in namespace boost::parameter unless otherwise specified.

Exceptions

No operation described in this document throws an exception unless otherwise specified.

Thread Safety

All components of this library can be used safely from multiple threads without synchronization. [#thread]_

Typography

Names written in :concept:sans serif type represent concepts_.

In code blocks, italic type represents unspecified text that satisfies the requirements given in the detailed description that follows the code block.

In a specification of the tokens generated by a macro, bold type is used to highlight the position of the expanded macro argument in the result.

The special character β represents the value of |BOOST_PARAMETER_MAX_ARITY|_.

//////////////////////////////////////////////////////////////////////////////

Terminology

.. |kw| replace:: keyword .. _kw:

keyword The name of a function parameter.

.. keyword tag type: .. |keyword tag type| replace:: keyword tag type

keyword tag type A type used to uniquely identify a function parameter. Typically its name will be the same as that of the parameter.

.. positional: .. |positional| replace:: positional

positional argument An argument passed with no explicit |kw|. Its parameter is determined in the usual C++ way: by position with respect to a parameter list.

.. tag type: .. |tag type| replace:: tag type

tag type Shorthand for “\ |keyword tag type|.”

.. keyword object: .. |keyword object| replace:: keyword object

keyword object An instance of |keyword|_\ <T> for some |tag type| T.

.. tagged reference: .. |tagged reference| replace:: tagged reference

tagged reference An object whose type is associated with a |keyword tag type| (the object's keyword), and that holds a reference (to the object's value).

As a shorthand, a “tagged reference to ``x``\ ” means a tagged reference
whose *value* is ``x``.

.. tagged default: .. |tagged default| replace:: tagged default

tagged default A |tagged reference| whose value represents the value of a default argument.

.. tagged lazy default: .. |tagged lazy default| replace:: tagged lazy default

tagged lazy default A |tagged reference| whose value, when invoked with no arguments, computes a default argument value.

.. intended argument type: .. |intended argument type| replace:: intended argument type

intended argument type The intended argument type of a single-element |ArgumentPack|_ is the type of its element's value. The intended argument type of any other type X is X itself.

.. Note::

In this reference, we will use concept names (and other names) to describe
both types and objects, depending on context.  So for example, “an
|ArgumentPack|_\ ” can refer to a type that models |ArgumentPack|_
*or* an object of such a type.

//////////////////////////////////////////////////////////////////////////////

Concepts

This section describes the generic type concepts used by the Parameter library.

|ArgumentPack|

Requirements ............

In the table below,

A is a model of |ArgumentPack|
x is an instance of A
u is a |keyword object| of type K
v is a |tagged default| with |tag type| L and value of type D
w is a |tagged lazy default| with |tag type| M and value of type E const
z is an |ArgumentPack| containing a single element (as created by |keyword|_\ <…>::operator=)

Any exceptions thrown from the invocation of w\ 's value will be propagated to the caller.

.. table:: |ArgumentPack| requirements

+------------+---------------------------------+----------------+----------------------+
| Expression | Type                            | Requirements   | Semantics/Notes      |
+============+=================================+================+======================+
|  ``x[u]``  | ``binding<A, K>::type``         | ``x`` contains | Returns *b*\ 's      |
|            |                                 | an element *b* | *value* (by          |
|            |                                 | whose |kw|_ is | reference).          |
|            |                                 | ``K``          |                      |
+------------+---------------------------------+----------------+----------------------+
|  ``x[u]``  | ``binding<A, L, D>::type``      | *none*         | If ``x`` contains an |
|            |                                 |                | element *b* whose    |
|            |                                 |                | |kw|_ is the same as |
|            |                                 |                | ``u``\ 's, returns   |
|            |                                 |                | *b*\ 's *value* (by  |
|            |                                 |                | reference).          |
|            |                                 |                | Otherwise, returns   |
|            |                                 |                | ``u``\ 's *value*.   |
+------------+---------------------------------+----------------+----------------------+
|  ``x[w]``  | ``lazy_binding<A, M, E>::type`` | *none*         | If ``x`` contains an |
|            |                                 |                | element *b* whose    |
|            |                                 |                | |kw|_ is the same as |
|            |                                 |                | ``w``\ 's, returns   |
|            |                                 |                | *b*\ 's *value* (by  |
|            |                                 |                | reference).          |
|            |                                 |                | Otherwise, invokes   |
|            |                                 |                | ``w``\ 's *value*    |
|            |                                 |                | and returns the      |
|            |                                 |                | result.              |
+------------+---------------------------------+----------------+----------------------+
|  ``x, z``  | Model of |ArgumentPack|_        | *none*         | Returns an           |
|            |                                 |                | |ArgumentPack|_      |
|            |                                 |                | containing all the   |
|            |                                 |                | elements of both     |
|            |                                 |                | ``x`` and ``z``.     |
+------------+---------------------------------+----------------+----------------------+

.. _parameterspec:

|ParameterSpec|

A |ParameterSpec| describes the type requirements for arguments corresponding to a given |kw|_ and indicates whether the argument is optional or required. The table below details the allowed forms and describes their condition for satisfaction by an actual argument type. In each row,

.. _conditions:

K is the |ParameterSpec|\ 's |keyword tag type|
A is an |intended argument type| associated with K, if any
P is a model of |ArgumentPack| that contains A
F is an MPL Binary Metafunction Class_

.. _MPL Binary Metafunction Class: ../../../mpl/doc/refmanual/metafunction-class.html

.. table:: |ParameterSpec| allowed forms and conditions of satisfaction

+------------------------+----------+----------------------------------------+
| Type                   | ``A``    | Condition ``A`` must satisfy           |
|                        | required |                                        |
+========================+==========+========================================+
| ``K``                  | no       |       *n/a*                            |
+------------------------+----------+----------------------------------------+
| |optional|_\ ``<K,F>`` | no       | ``mpl::apply2<F,A,P>::type::value`` is |
|                        |          | ``true``.                              |
+------------------------+----------+----------------------------------------+
| |required|_\ ``<K,F>`` | yes      | ``mpl::apply2<F,A,P>::type::value`` is |
|                        |          | ``true``.                              |
+------------------------+----------+----------------------------------------+

The information in a |ParameterSpec| is used to limit__ the arguments that will be matched by forwarding functions_.

__ overloadcontrol_ .. _overloadcontrol: index.html#controlling-overload-resolution .. _forwarding functions: index.html#forwarding-functions

//////////////////////////////////////////////////////////////////////////////

Class Templates

.. |keyword| replace:: keyword .. _keyword:

`keyword`

The type of every |keyword object| is a specialization of |keyword|.

:Defined in: |keyword_header|_

.. parsed-literal::

template <typename Tag>
struct keyword
{
    typedef Tag tag;

    template <typename T>
    constexpr typename |boost_enable_if|_\<
        typename |mpl_eval_if|_\<
            |boost_is_scalar|_\<T>
          , |mpl_true|_\  // Enable this overload for scalar types.
          , |mpl_eval_if|_\<
                |boost_is_same|_\<
                    typename Tag\:\:qualifier
                  , boost::parameter::in_reference
                >
              , |mpl_true|_\  // Enable this overload for "in" references.
              , |mpl_if|_\<
                    |boost_is_same|_\<
                        typename Tag\:\:qualifier
                      , boost::parameter::forward_reference
                    >
                  , |mpl_true|_\  // Enable this overload for "forward" references.
                  , |mpl_false|_\  // Disable this overload for all other reference categories.
                >
            >
        >::type
      , |ArgumentPack|_
    >::type
        |assignment operator|_\(T const& value) const;

    template <typename T>
    constexpr typename |boost_enable_if|_\<
        typename |mpl_eval_if|_\<
            typename |mpl_eval_if|_\<
                |boost_is_same|_\<
                    typename Tag\:\:qualifier
                  , boost::parameter::out_reference
                >
              , |mpl_true|_\  // The reference category is "out".
              , |mpl_if|_\<
                    |boost_is_same|_\<
                        typename Tag\:\:qualifier
                      , boost::parameter::forward_reference
                    >
                  , |mpl_true|_\  // The reference category is "forward".
                  , |mpl_false|_\  // The reference category is neither "out" nor "forward".
                >
            >::type
          , |mpl_if|_\<
                |boost_is_const|_\<T>
              , |mpl_false|_\  // Disable this overload for reference-to-const types.
              , |mpl_true|_\  // Enable this overload for referece-to-mutable types.
            >
          , |mpl_false|_\  // Disable this overload for references neither "out" nor "forward".
        >::type
      , |ArgumentPack|_
    >::type
        |assignment operator|_\(T& value) const;

    template <typename T>
    constexpr typename |boost_enable_if|_\<
        typename |mpl_eval_if|_\<
            |boost_is_scalar|_\<T>
          , |mpl_false|_\  // Disable this overload for scalar types.
          , |mpl_eval_if|_\<
                |boost_is_same|_\<
                    typename Tag\:\:qualifier
                  , boost::parameter::in_reference
                >
              , |mpl_true|_\  // Enable this overload for "in" references.
              , |mpl_if|_\<
                    |boost_is_same|_\<
                        typename Tag\:\:qualifier
                      , boost::parameter::forward_reference
                    >
                  , |mpl_true|_\  // Enable this overload for "forward" references.
                  , |mpl_false|_\  // Disable this overload for all other reference categories.
                >
            >
        >::type
      , |ArgumentPack|_
    >::type
        |assignment operator|_\(T const&& value) const;

    template <typename T>
    constexpr typename |boost_enable_if|_\<
        typename |mpl_eval_if|_\<
            |boost_is_scalar|_\<T>
          , |mpl_false|_\  // Disable this overload for scalar types.
          , |mpl_eval_if|_\<
                |boost_is_same|_\<
                    typename Tag\:\:qualifier
                  , boost::parameter::consume_reference
                >
              , |mpl_true|_\  // Enable this overload for "consume" references.
              , |mpl_if|_\<
                    |boost_is_same|_\<
                        typename Tag\:\:qualifier
                      , boost::parameter::forward_reference
                    >
                  , |mpl_true|_\  // Enable this overload for "forward" references.
                  , |mpl_false|_\  // Disable this overload for all other reference categories.
                >
            >
        >::type
      , |ArgumentPack|_
    >::type
        |assignment operator|_\(T&& value) const;

    template <typename T>
    constexpr typename |boost_enable_if|_\<
        typename |mpl_eval_if|_\<
            |boost_is_scalar|_\<T>
          , |mpl_true|_\  // Enable this overload for scalar types.
          , |mpl_eval_if|_\<
                |boost_is_same|_\<
                    typename Tag\:\:qualifier
                  , boost::parameter::in_reference
                >
              , |mpl_true|_\  // Enable this overload for "in" references.
              , |mpl_if|_\<
                    |boost_is_same|_\<
                        typename Tag\:\:qualifier
                      , boost::parameter::forward_reference
                    >
                  , |mpl_true|_\  // Enable this overload for "forward" references.
                  , |mpl_false|_\  // Disable this overload for all other reference categories.
                >
            >
        >::type
      , *tagged default*
    >::type
        |bitwise or operator|_\(T const& x) const;

    template <typename T>
    constexpr typename |boost_enable_if|_\<
        typename |mpl_eval_if|_\<
            typename |mpl_eval_if|_\<
                |boost_is_same|_\<
                    typename Tag\:\:qualifier
                  , boost::parameter::out_reference
                >
              , |mpl_true|_\  // The reference category is "out".
              , |mpl_if|_\<
                    |boost_is_same|_\<
                        typename Tag\:\:qualifier
                      , boost::parameter::forward_reference
                    >
                  , |mpl_true|_\  // The reference category is "forward".
                  , |mpl_false|_\  // The reference category is neither "out" nor "forward".
                >
            >::type
          , |mpl_if|_\<
                |boost_is_const|_\<T>
              , |mpl_false|_\  // Disable this overload for reference-to-const types.
              , |mpl_true|_\  // Enable this overload for referece-to-mutable types.
            >
          , |mpl_false|_\  // Disable this overload for references neither "out" nor "forward".
        >::type
      , *tagged default*
    >::type
        |bitwise or operator|_\(T& x) const;

    template <typename T>
    constexpr typename |boost_enable_if|_\<
        typename |mpl_eval_if|_\<
            |boost_is_scalar|_\<T>
          , |mpl_false|_\  // Disable this overload for scalar types.
          , |mpl_eval_if|_\<
                |boost_is_same|_\<
                    typename Tag\:\:qualifier
                  , boost::parameter::in_reference
                >
              , |mpl_true|_\  // Enable this overload for "in" references.
              , |mpl_if|_\<
                    |boost_is_same|_\<
                        typename Tag\:\:qualifier
                      , boost::parameter::forward_reference
                    >
                  , |mpl_true|_\  // Enable this overload for "forward" references.
                  , |mpl_false|_\  // Disable this overload for all other reference categories.
                >
            >
        >::type
      , *tagged default*
    >::type
        |bitwise or operator|_\(T const&& x) const;

    template <typename T>
    constexpr typename |boost_enable_if|_\<
        typename |mpl_eval_if|_\<
            |boost_is_scalar|_\<T>
          , |mpl_false|_\  // Disable this overload for scalar types.
          , |mpl_eval_if|_\<
                |boost_is_same|_\<
                    typename Tag\:\:qualifier
                  , boost::parameter::consume_reference
                >
              , |mpl_true|_\  // Enable this overload for "consume" references.
              , |mpl_if|_\<
                    |boost_is_same|_\<
                        typename Tag\:\:qualifier
                      , boost::parameter::forward_reference
                    >
                  , |mpl_true|_\  // Enable this overload for "forward" references.
                  , |mpl_false|_\  // Disable this overload for all other reference categories.
                >
            >
        >::type
      , *tagged default*
    >::type constexpr
        |bitwise or operator|_\(T&& value) const;

    template <typename F>
    constexpr *tagged lazy default* |logical or operator|_\(F const&) const;

    template <typename F>
    constexpr *tagged lazy default* |logical or operator|_\(F&) const;

    static keyword<Tag> const& instance;

    static keyword<Tag>& get_\();
};

.. |assignment operator| replace:: operator= .. _assignment operator:

operator=

:Synopsis:

.. parsed-literal::

template <typename T>
constexpr |ArgumentPack|_ operator=(T const& value) const;

template <typename T>
constexpr |ArgumentPack|_ operator=(T& value) const;

template <typename T>
constexpr |ArgumentPack|_ operator=(T const&& value) const;

template <typename T>
constexpr |ArgumentPack|_ operator=(T&& value) const;

:Requires: one of the following:

The nested qualifier type of Tag must be forward_reference.
To use the const lvalue reference overload, T must be scalar, or the nested qualifier type of Tag must be in_reference.
To use the mutable lvalue reference overload, the nested qualifier type of Tag must be out_reference or in_out_reference, and T must not be const-qualified.
To use the const rvalue reference overload for non-scalar T, the nested qualifier type of Tag must be in_reference.
To use the mutable rvalue reference overload for non-scalar T, the nested qualifier type of Tag must be consume_reference or move_from_reference.

.. |bitwise or operator| replace:: operator| .. _bitwise or operator:

operator|

:Synopsis:

.. parsed-literal::

template <typename T>
constexpr *tagged default* operator|(T const& x) const;

template <typename T>
constexpr *tagged default* operator|(T& x) const;

template <typename T>
constexpr *tagged default* operator|(T const&& x) const;

template <typename T>
constexpr *tagged default* operator|(T&& x) const;

:Requires: one of the following:

The nested qualifier type of Tag must be forward_reference.
To use the const lvalue reference overload, T must be scalar, or the nested qualifier type of Tag must be in_reference.
To use the mutable lvalue reference overload, the nested qualifier type of Tag must be out_reference or in_out_reference, and T must not be const-qualified.
To use the const rvalue reference overload for non-scalar T, the nested qualifier type of Tag must be in_reference.
To use the mutable rvalue reference overload for non-scalar T, the nested qualifier type of Tag must be consume_reference or move_from_reference.

:Returns: a |tagged default| with value x and |kw|_ Tag.

.. |logical or operator| replace:: operator|| .. _logical or operator:

operator||

:Synopsis:

.. parsed-literal::

template <typename F>
constexpr *tagged lazy default* operator||(F const& g) const;

template <typename F>
constexpr *tagged lazy default* operator||(F& g) const;

:Requires: g() must be valid, with type |boost_result_of|\ <F()>::type. [#no_result_of]

:Returns: a |tagged lazy default| with value g and |kw|_ Tag.

.. _instance:

instance

:Synopsis:

.. parsed-literal::

static keyword<Tag> const& instance;

:Returns: a “singleton instance”: the same object will be returned on each invocation of instance.

:Thread Safety: instance can be accessed from multiple threads simultaneously.

.. _get:

get

:Synopsis:

.. parsed-literal::

static keyword<Tag>& get\();

.. admonition:: Deprecated

This function has been deprecated in favor of ``instance``.

:Returns: a “singleton instance”: the same object will be returned on each invocation of get().

:Thread Safety: get() can be called from multiple threads simultaneously.

.. |template_keyword| replace:: template_keyword .. _template_keyword:

`template_keyword`

This class template encapsulates a named template parameter. Every type generated by the |BOOST_PARAMETER_TEMPLATE_KEYWORD|_ macro is a specialization of |template_keyword|.

:Defined in: |template_keyword_header|_

.. parsed-literal::

template <typename Tag, typename T>
struct template_keyword
{
    typedef Tag key_type;
    typedef T value_type;
    typedef *implementation defined* reference;
};

The |ntp_cpp|_ test program demonstrates proper usage of this class template.

.. |parameters| replace:: parameters .. _parameters:

`parameters`

Provides an interface for assembling the actual arguments to a forwarding function into an |ArgumentPack|, in which any |positional| arguments will be tagged according to the corresponding template argument to parameters.

.. forwarding function: forwarding functions

:Defined in: |parameters_header|_

.. parsed-literal::

template <typename ...PSpec>
struct parameters
{
    template <typename ...Args>
    struct |match|_
    {
        typedef … type;
    };

    template <typename ...Args>
    |ArgumentPack|_ |function call operator|_\(Args&&... args) const;
};

:Requires: Each element in the PSpec parameter pack must be a model of |ParameterSpec|_.

.. Note::

In this section, ``R`` ## *i* and ``K`` ## *i* are defined as
follows, for any argument type ``A`` ## *i*:

| let ``D0`` the set [d0, …, d ## *j*] of all **deduced**
| *parameter specs* in the ``PSpec`` parameter pack
| ``R`` ## *i* is the |intended argument type| of ``A`` ## *i*
|
| if ``A`` ## *i* is a result type of ``keyword<T>::`` |assignment operator|_
| then 
|     ``K`` ## *i* is ``T``
| else
|     if some ``A`` ## *j* where *j* ≤ *i* is a result type of
|     ``keyword<T>::`` |assignment operator|_
|     *or* some ``P`` ## *j* in *j* ≤ *i* is **deduced**
|     then
|         if some *parameter spec* ``d`` ## *j* in ``D`` ## *i*
|         matches ``A`` ## *i*
|         then
|             ``K`` ## *i* is the |keyword tag type| of ``d`` ## *j*.
|             ``D``:sub:`i+1` is ``D`` ## *i* - [ ``d`` ## *j*]
|     else
|         ``K`` ## *i* is the |keyword tag type| of ``P`` ## *i*.

.. |match| replace:: match .. _match:

match A Metafunction_ used to remove a forwarding function_ from overload resolution.

:Returns: if all elements in Params... are satisfied (see below), then parameters<Params...>. Otherwise, match<Args...>::type is not defined.

Each element P in Params... is satisfied if either:

P is the unspecified default
or, P is a keyword tag type
or, P is |optional|_ <X,F> and either
- X is not K ## i for any i,
- or X is some K ## i and mpl::apply<F,R ## i
  >::type::value is true
or, P is |required|_ <X,F>, and
- X is some K ## i, and
- mpl::apply<F,R ## i >::type::value is true

.. |function call operator| replace:: operator() .. _function call operator:

operator()

:Synopsis:

.. parsed-literal::

template <typename ...Args>
|ArgumentPack|_ operator()(Args&&... args) const;

:Returns: An |ArgumentPack|_ containing, for each a ## i,

- if ``a`` ## *i*  is a single-element |ArgumentPack|, its element
- Otherwise, a |tagged reference| with |kw|_ ``K`` ## *i* and *value*
    ``a`` ## *i*

.. |optional| replace:: optional .. |required| replace:: required

.. _optional: .. _required:

`optional`, `required`

These templates describe the requirements on a function parameter.

optional is defined in: |optional_header|_

required is defined in: |required_header|_

Both headers are included by: |preprocessor_header|_

:Specializations model: |ParameterSpec|_

.. parsed-literal::

template <typename Tag, typename Predicate = *unspecified*>
struct optional;

template <typename Tag, typename Predicate = *unspecified*>
struct required;

The default value of Predicate is an unspecified MPL Binary Metafunction Class_ that returns mpl::true_ for any argument. If |BOOST_PARAMETER_CAN_USE_MP11|_ is defined, then the default value of Predicate is also a |Boost_MP11|_-style quoted metafunction that returns mp11::mp_true for any argument.

.. |deduced| replace:: deduced .. _deduced:

`deduced`

This template is used to wrap the keyword tag argument to optional or required.

:Defined in: |deduced_header|_ :Included by: |preprocessor_header|_

.. parsed-literal::

template <typename Tag>
struct deduced;

:Requires: nothing

//////////////////////////////////////////////////////////////////////////////

Metafunctions

A Metafunction_ is conceptually a function that operates on, and returns, C++ types.

.. |binding| replace:: binding .. _binding:

`binding`

Returns the result type of indexing an argument pack with a |keyword tag type| or with a |tagged default|.

:Defined in: |binding_header|_

.. parsed-literal::

template <typename A, typename K, typename D = void\_>
struct binding
{
    typedef … type;
};

:Requires: A must be a model of |ArgumentPack|_.

.. |lazy_binding| replace:: lazy_binding .. _lazy_binding:

`lazy_binding`

Returns the result type of indexing an argument pack with a |tagged lazy default|.

:Defined in: |binding_header|_

.. parsed-literal::

template <typename A, typename K, typename F>
struct lazy_binding
{
    typedef … type;
};

:Requires: A must be a model of |ArgumentPack|_.

.. |value_type| replace:: value_type .. _value_type:

`value_type`

Returns the result type of indexing an argument pack with a |keyword tag type| or with a |tagged default|.

:Defined in: |value_type_header|_

.. parsed-literal::

template <typename A, typename K, typename D = void\_>
struct value_type
{
    typedef … type;
};

:Requires: A must be a model of |ArgumentPack|_.

.. parsed-literal::

    typename |boost_remove_reference|_\<
        typename |binding|_\<A, K, D>::type
    >::type

… when ``D`` is not a reference type.

.. |lazy_value_type| replace:: lazy_value_type .. _lazy_value_type:

`lazy_value_type`

Returns the result type of indexing an argument pack with a |tagged lazy default|.

:Defined in: |value_type_header|_

.. parsed-literal::

template <typename A, typename K, typename F>
struct lazy_value_type
{
    typedef … type;
};

:Requires: A must be a model of |ArgumentPack|_.

.. |are_tagged_arguments| replace:: are_tagged_arguments .. _are_tagged_arguments:

`are_tagged_arguments`

:Defined in: |are_tagged_arguments_header|_

.. parsed-literal::

template <typename T0, typename ...Pack>
struct are_tagged_arguments
    // : |mpl_true|_\  if T0 and all elements in Pack are
    // tagged reference types, |mpl_false|_\  otherwise.
{
};

:Returns: mpl::true_ if T0 and all elements in parameter pack Pack are |tagged reference| types, mpl::false_ otherwise.

:Example usage:

When implementing a Boost.Parameter-enabled constructor for a container that conforms to the C++ standard, one needs to remember that the standard requires the presence of other constructors that are typically defined as templates, such as range constructors. To avoid overload ambiguities between the two constructors, use this metafunction in conjunction with disable_if to define the range constructor.

.. parsed-literal::

template <typename B>
class frontend : public B
{
    struct _enabler
    {
    };

 public:
    |BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR|_\(frontend, (B))

    template <typename Iterator>
    frontend(
        Iterator itr
      , Iterator itr_end
      , typename |boost_disable_if|_\<
            are_tagged_arguments<Iterator>
          , _enabler
        >::type = _enabler()
    ) : B(itr, itr_end)
    {
    }
};

.. |is_argument_pack| replace:: is_argument_pack .. _is_argument_pack:

`is_argument_pack`

:Defined in: |is_argument_pack_header|_

.. parsed-literal::

template <typename T>
struct is_argument_pack
    // : |mpl_true|_\  if T is a model of |ArgumentPack|_\,
    // |mpl_false|_\  otherwise.
{
};

:Returns: mpl::true_ if T is a model of |ArgumentPack|_, mpl::false_ otherwise.

:Example usage:

To avoid overload ambiguities between a constructor that takes in an |ArgumentPack|_ and a templated conversion constructor, use this metafunction in conjunction with enable_if.

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\(a0)

template <typename T>
class backend0
{
    struct _enabler
    {
    };

    T a0;

 public:
    template <typename ArgPack>
    explicit backend0(
        ArgPack const& args
      , typename |boost_enable_if|_\<
            is_argument_pack<ArgPack>
          , _enabler
        >::type = _enabler()
    ) : a0(args[_a0])
    {
    }

    template <typename U>
    backend0(
        backend0<U> const& copy
      , typename |boost_enable_if|_\<
            |boost_is_convertible|_\<U,T>
          , _enabler
        >::type = _enabler()
    ) : a0(copy.get_a0())
    {
    }

    T const& get_a0() const
    {
        return this->a0;
    }
};

.. |result_of_compose| replace:: result_of::compose .. _result_of_compose:

`result_of::compose`

Returns the result type of the |compose|_ function.

:Defined in: |compose_header|_

.. parsed-literal::

template <typename ...TaggedArgs>
struct compose
  : |boost_enable_if|_\<
        |are_tagged_arguments|_\<T0,Pack...>
      , |ArgumentPack|_
    >
{
};

template <>
struct compose<>
{
    typedef *empty* |ArgumentPack|_ type;
};

:Requires: All elements in TaggedArgs must be |tagged reference| types, if specified.

:Returns: the result type of the |compose|_ function.

//////////////////////////////////////////////////////////////////////////////

Function Templates

.. |compose| replace:: compose .. _compose:

`compose`

:Defined in: |compose_header|_

.. parsed-literal::

template <typename ...Pack>
constexpr typename |result_of_compose|_\<Pack...>::type
    compose(Pack const&... args);

Unlike the |tagged reference| comma operator, the compose() function is variadic, as mentioned before. However, the |tagged reference| comma operator can be invoked indefinitely and therefore does not limit the size of the resulting |ArgumentPack|, while the compose() function cannot take in more than |BOOST_PARAMETER_COMPOSE_MAX_ARITY|_ arguments for compilers that do not support perfect forwarding.

:Requires: All elements in args must be |tagged reference| objects, if specified.

:Returns: an |ArgumentPack|_ containing all elements in args, if specified; an empty |ArgumentPack|_ otherwise.

:Example usage:

.. parsed-literal::

BOOST_PARAMETER_NAME(index)
BOOST_PARAMETER_NAME(name)

template <typename ArgumentPack>
int print_name_and_index(ArgumentPack const& args)
{
    std::cout << "index = " << args[_index];
    std::cout << "name = " << args[_name];
    std::cout << "; " << std::endl;
    return 0;
}

int y = print_name_and_index(compose(_index = 3, _name = "jones"));

The |compose_cpp|_ test program shows more examples using this function.

//////////////////////////////////////////////////////////////////////////////

Code Generation Macros

Macros in this section can be used to ease the writing of code using the Parameter library by eliminating repetitive boilerplate.

.. |BOOST_PARAMETER_FUNCTION| replace:: BOOST_PARAMETER_FUNCTION .. _BOOST_PARAMETER_FUNCTION:

`BOOST_PARAMETER_FUNCTION(result, name, tag_namespace, arguments)`

:Defined in: |preprocessor_header|_

Generates a function that can take in positional arguments, composed arguments, named arguments, and deduced arguments.

:Example usage:

The return type of each of the following function templates falls under a different value category.

.. parsed-literal::

template <std::size_t N>
|std_bitset|_\<N + 1> rvalue_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1> const rvalue_const_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1>& lvalue_bitset()
{
    static |std_bitset|_\<N + 1> lset = |std_bitset|_\<N + 1>();
    return lset;
}

template <std::size_t N>
|std_bitset|_\<N + 1> const& lvalue_const_bitset()
{
    static |std_bitset|_\<N + 1> const clset = |std_bitset|_\<N + 1>();
    return clset;
}

The U::evaluate_category static member function template has a simple job: to return the correct value category when passed in an object returned by one of the functions defined above. Assume that |BOOST_PARAMETER_HAS_PERFECT_FORWARDING|_ is defined.

.. parsed-literal::

enum invoked
{
    passed_by_lvalue_reference_to_const
  , passed_by_lvalue_reference
  , passed_by_rvalue_reference_to_const
  , passed_by_rvalue_reference
};

struct U
{
    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&)
    {
        return passed_by_lvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&)
    {
        return passed_by_lvalue_reference;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&&)
    {
        return passed_by_rvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&&)
    {
        return passed_by_rvalue_reference;
    }
};

Define the named parameters that will comprise the argument specification that this macro will use. Ensure that all their tag types are in the same namespace, which is kw in this case. The identifiers with leading underscores can be passed to the bracket operator of args to extract the same argument to which the corresponding named parameter (without underscores) is bound, as will be shown later.

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\((_lrc, kw) in(lrc))
|BOOST_PARAMETER_NAME|_\((_lr, kw) in_out(lr))
|BOOST_PARAMETER_NAME|_\((_rrc, kw) in(rrc))
|BOOST_PARAMETER_NAME|_\((_rr, kw) consume(rr))

Use the macro as a substitute for a normal function header. Enclose the return type bool in parentheses. For each parameter, also enclose the expected value type in parentheses. Since the value types are mutually exclusive, you can wrap the parameters in a (deduced …) clause. Otherwise, just as with a normal function, the order in which you specify the parameters determines their position. Also, just as with a normal function, optional parameters have default values, whereas required parameters do not. Within the function body, either simply use the parameter name or pass the matching identifier with the leading underscore to the bracket operator of args to extract the corresponding argument. Note that the second method doesn't require std::forward to preserve value categories.

.. parsed-literal::

BOOST_PARAMETER_FUNCTION((bool), evaluate, kw,
    (deduced
        (required
            (lrc, (|std_bitset|_\<1>))
            (lr, (|std_bitset|_\<2>))
        )
        (optional
            (rrc, (|std_bitset|_\<3>), rvalue_const_bitset<2>())
            (rr, (|std_bitset|_\<4>), rvalue_bitset<3>())
        )
    )
)
{
    BOOST_TEST_EQ(
        passed_by_lvalue_reference_to_const
      , U::evaluate_category<0>(lrc)
    );
    BOOST_TEST_EQ(
        passed_by_lvalue_reference
      , U::evaluate_category<1>(lr)
    );
    BOOST_TEST_EQ(
        passed_by_rvalue_reference_to_const
      , U::evaluate_category<2>(|std_forward|_\<rrc0_type>(rrc0))
    );
    BOOST_TEST_EQ(
        passed_by_rvalue_reference
      , U::evaluate_category<3>(args[_rr0])
    );

    return true;
}

The following function calls are legal.

.. parsed-literal::

evaluate(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
  , rvalue_bitset<3>()
);
evaluate(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
);
evaluate((  // composed arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
));
evaluate(  // named arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
);
evaluate(  // named arguments
    _lr0 = lvalue_bitset<1>()
  , _lrc0 = lvalue_const_bitset<0>()
);

Because the parameters were wrapped in a (deduced …) clause, the following function calls are also legal.

.. parsed-literal::

evaluate(  // deduced arguments
    rvalue_bitset<3>()
  , lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
);
evaluate(  // deduced arguments
    lvalue_bitset<1>()
  , lvalue_const_bitset<0>()
);

The |preprocessor_cpp|, |preprocessor_deduced_cpp|, and |preprocessor_eval_cat_cpp|_ test programs demonstrate proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function.
name is the base name of the function; it determines the name of the generated forwarding functions.
tag_namespace is the namespace in which the keywords used by the function resides.
arguments is a |Boost_Preprocessor|_ sequence_ of argument-specifiers, as defined below.

Argument specifiers syntax:

.. parsed-literal::

argument-specifiers ::= *specifier-group0* {*specifier-group0*\ }

specifier-group0 ::= *specifier-group1* |
    (
        '**(**' '**deduced**'
            *specifier-group1* {*specifier-group1*\ }
        '**)**'
    )

specifier-group1 ::=
    (
        '**(**' '**optional**'
            *optional-specifier* {*optional-specifier*\ }
        '**)**'
    ) | (
        '**(**' '**required**'
            *required-specifier* {*required-specifier*\ }
        '**)**'
    )

optional-specifier ::=
    '**(**'
        *argument-name* '**,**' *restriction* '**,**' *default-value*
    ')'

required-specifier ::=
    '**(**' *argument-name* '**,**' *restriction* ')'

restriction ::=
    ( '**\***' '**(**' *mfc* '**)**' ) |
    ( '**(**' *type-name* '**)**' ) |
    '**\***'

argument-name is any valid C++ identifier.
default-value is any valid C++ expression; if necessary, user code can compute it in terms of previous-name ## _type, where previous-name is the argument-name in a previous specifier-group0 or specifier-group1. This expression will be invoked exactly once.
mfc is an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|, and whose return type is a Boolean Integral Constant; however, user code cannot compute mfc in terms of previous-name ## _type.
type-name is either the name of a target type or an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|_, and whose return type is the target type. If restriction uses this form, then the type of the generated name argument-name ## _type will be computed in terms of the target type, and the generated reference argument-name (but not its corresponding entry in args) will be cast to that type.

Approximate expansion:

Where:

n denotes the minimum arity, as determined from arguments.
m denotes the maximum arity, as determined from arguments.

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename Args>
using boost_param_result\_ ## __LINE__ ## **name** = **result**;

// If **result** is a simple return type:
template <typename Args>
struct boost_param_result\_ ## __LINE__ ## **name**
{
    typedef **result** type;
};

struct boost_param_params\_ ## __LINE__ ## **name**
  : |parameters|_\<
        *list of parameter specifications, based on arguments*
    >
{
};

typedef boost_param_params\_ ## __LINE__ ## **name**
    boost_param_parameters\_ ## __LINE__ ## **name**;

template <typename Args>
typename boost_param_result\_ ## __LINE__ ## **name**\ <Args>::type
    boost_param_impl ## __LINE__ ## **name**\ (Args const&);

template <typename A0, …, typename A ## **n**>
**result** **name**\ (
    A0&& a0, …, A ## **n**\ && a ## **n**
  , typename boost_param_parameters\_ ## __LINE__ ## **name**
    ::match<A0, …, A ## **n**>::type
    = boost_param_parameters\_ ## __LINE__ ## **name**\ ()
)
{
    return boost_param_impl ## __LINE__ ## **name**\ (
        boost_param_parameters\_ ## __LINE__ ## **name**\ ()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **n**>(a ## **n**)
        )
    );
}

:vellipsis:`⋮`

template <typename A0, …, typename A ## **m**>
**result** **name**\ (
    A0&& a0, …, A ## **m**\ && a ## **m**
  , typename boost_param_parameters\_ ## __LINE__ ## **name**
    ::match<A0, …, A ## **m**>::type
    = boost_param_parameters\_ ## __LINE__ ## **name**\ ()
)
{
    return boost_param_impl ## __LINE__ ## **name**\ (
        boost_param_parameters\_ ## __LINE__ ## **name**\ ()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **m**>(a ## **m**)
        )
    );
}

template <
    typename ResultType
  , typename Args
  , typename *argument name* ## **0** ## _type
  , …
  , typename *argument name* ## **n** ## _type
>
ResultType
    boost_param_dispatch_0boost\_ ## __LINE__ ## **name**\ (
        (ResultType(*)())
      , Args const& args
      , *argument name* ## **0** ## _type&& *argument name* ## **0**
      , …
      , *argument name* ## **n** ## _type&& *argument name* ## **m**
    );

:vellipsis:`⋮`

template <
    typename ResultType
  , typename Args
  , typename *argument name* ## **0** ## _type
  , …
  , typename *argument name* ## **m** ## _type
>
ResultType
    boost_param_dispatch_0boost\_ ## __LINE__ ## **name**\ (
        (ResultType(*)())
      , Args const& args
      , *argument name* ## **0** ## _type&& *argument name* ## **0**
      , …
      , *argument name* ## **m** ## _type&& *argument name* ## **m**
    );

template <typename Args>
typename boost_param_result\_ ## __LINE__ ## **name**\ <Args>::type
    boost_param_impl ## __LINE__ ## **name**\ (Args const& args)
{
    return boost_param_dispatch_0boost\_ ## __LINE__ ## **name**\ (
        static_cast<
            typename boost_param_result\_ ## __LINE__ ## **name**\ <
                Args
            >::type(*)()
        >(|std_nullptr|_\)
      , args
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of required parameter* ## **0**
            >::type
        >(args[ *keyword object of required parameter* ## **0**])
      , …
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of required parameter* ## **n**
            >::type
        >(args[ *keyword object of required parameter* ## **n**])
    );
}

template <
    typename ResultType
  , typename Args
  , typename *argument name* ## **0** ## _type
  , …
  , typename *argument name* ## **n** ## _type
>
ResultType
    boost_param_dispatch_0boost\_ ## __LINE__ ## **name**\ (
        (ResultType(*)())
      , Args const& args
      , *argument name* ## **0** ## _type&& *argument name* ## **0**
      , …
      , *argument name* ## **n** ## _type&& *argument name* ## **n**
    )
{
    return boost_param_dispatch_0boost\_ ## __LINE__ ## **name**\ (
        static_cast<ResultType(*)()>(|std_nullptr|_\)
      , (args, *keyword object of optional parameter* ## **n + 1** =
            *default value of optional parameter* ## **n + 1**
        )
      , |std_forward|_\<*argument name* ## **0** ## _type>(
            *argument name* ## **0**
        )
      , …
      , |std_forward|_\<*argument name* ## **n** ## _type>(
            *argument name* ## **n**
        )
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of optional parameter* ## **n + 1**
            >::type
        >(*default value of optional parameter* ## **n + 1**)
    );
}

:vellipsis:`⋮`

template <
    typename ResultType
  , typename Args
  , typename *argument name* ## **0** ## _type
  , …
  , typename *argument name* ## **m** ## _type
>
ResultType
    boost_param_dispatch_0boost\_ ## __LINE__ ## **name**\ (
        (ResultType(*)())
      , Args const& args
      , *argument name* ## **0** ## _type&& *argument name* ## **0**
      , …
      , *argument name* ## **m** ## _type&& *argument name* ## **m**
    )

.. |BOOST_PARAMETER_MEMBER_FUNCTION| replace:: BOOST_PARAMETER_MEMBER_FUNCTION .. _BOOST_PARAMETER_MEMBER_FUNCTION:

`BOOST_PARAMETER_MEMBER_FUNCTION(result, name, tag_namespace, arguments)`

:Defined in: |preprocessor_header|_

Generates a member function that can take in positional arguments, composed arguments, named arguments, and deduced arguments.

:Example usage:

The return type of each of the following function templates falls under a different value category.

.. parsed-literal::

template <std::size_t N>
|std_bitset|_\<N + 1> rvalue_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1> const rvalue_const_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1>& lvalue_bitset()
{
    static |std_bitset|_\<N + 1> lset = |std_bitset|_\<N + 1>();
    return lset;
}

template <std::size_t N>
|std_bitset|_\<N + 1> const& lvalue_const_bitset()
{
    static |std_bitset|_\<N + 1> const clset = |std_bitset|_\<N + 1>();
    return clset;
}

.. parsed-literal::

enum invoked
{
    passed_by_lvalue_reference_to_const
  , passed_by_lvalue_reference
  , passed_by_rvalue_reference_to_const
  , passed_by_rvalue_reference
};

struct U
{
    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&)
    {
        return passed_by_lvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&)
    {
        return passed_by_lvalue_reference;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&&)
    {
        return passed_by_rvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&&)
    {
        return passed_by_rvalue_reference;
    }
};

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\((_lrc, kw) in(lrc))
|BOOST_PARAMETER_NAME|_\((_lr, kw) in_out(lr))
|BOOST_PARAMETER_NAME|_\((_rrc, kw) in(rrc))
|BOOST_PARAMETER_NAME|_\((_rr, kw) consume(rr))

Use the macro as a substitute for a normal static member function header. Enclose the return type bool in parentheses. For each parameter, also enclose the expected value type in parentheses. Since the value types are mutually exclusive, you can wrap the parameters in a (deduced …) clause. Otherwise, just as with a normal function, the order in which you specify the parameters determines their position. Also, just as with a normal function, optional parameters have default values, whereas required parameters do not. Within the function body, either simply use the parameter name or pass the matching identifier with the leading underscore to the bracket operator of args to extract the corresponding argument. Note that the second method doesn't require std::forward to preserve value categories.

.. parsed-literal::

struct B
{
    BOOST_PARAMETER_MEMBER_FUNCTION((bool), static evaluate, kw,
        (deduced
            (required
                (lrc, (|std_bitset|_\<1>))
                (lr, (|std_bitset|_\<2>))
            )
            (optional
                (rrc, (|std_bitset|_\<3>), rvalue_const_bitset<2>())
                (rr, (|std_bitset|_\<4>), rvalue_bitset<3>())
            )
        )
    )
    {
        BOOST_TEST_EQ(
            passed_by_lvalue_reference_to_const
          , U::evaluate_category<0>(lrc)
        );
        BOOST_TEST_EQ(
            passed_by_lvalue_reference
          , U::evaluate_category<1>(lr)
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference_to_const
          , U::evaluate_category<2>(|std_forward|_\<rrc0_type>(rrc0))
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference
          , U::evaluate_category<3>(args[_rr0])
        );

        return true;
    }
};

The following function calls are legal.

.. parsed-literal::

B::evaluate(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
  , rvalue_bitset<3>()
);
B::evaluate(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
);
B::evaluate((  // composed arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
));
B::evaluate(  // named arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
);
B::evaluate(  // named arguments
    _lr0 = lvalue_bitset<1>()
  , _lrc0 = lvalue_const_bitset<0>()
);

Because the parameters were wrapped in a (deduced …) clause, the following function calls are also legal.

.. parsed-literal::

B::evaluate(  // deduced arguments
    rvalue_bitset<3>()
  , lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
);
B::evaluate(  // deduced arguments
    lvalue_bitset<1>()
  , lvalue_const_bitset<0>()
);

The |preprocessor_cpp|_ and |preprocessor_eval_cat_cpp|_ test programs demonstrate proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function.
name is the base name of the function; it determines the name of the generated forwarding functions. name may be qualified by the static keyword to declare the member function and its helpers as not associated with any object of the enclosing type.
tag_namespace is the namespace in which the keywords used by the function resides.
arguments is a |Boost_Preprocessor|_ sequence_ of argument-specifiers, as defined below.

Argument specifiers syntax:

.. parsed-literal::

argument-specifiers ::= *specifier-group0* {*specifier-group0*\ }

specifier-group0 ::= *specifier-group1* |
    (
        '**(**' '**deduced**'
            *specifier-group1* {*specifier-group1*\ }
        '**)**'
    )

specifier-group1 ::=
    (
        '**(**' '**optional**'
            *optional-specifier* {*optional-specifier*\ }
        '**)**'
    ) | (
        '**(**' '**required**'
            *required-specifier* {*required-specifier*\ }
        '**)**'
    )

optional-specifier ::=
    '**(**'
        *argument-name* '**,**' *restriction* '**,**' *default-value*
    ')'

required-specifier ::=
    '**(**' *argument-name* '**,**' *restriction* ')'

restriction ::=
    ( '**\***' '**(**' *mfc* '**)**' ) |
    ( '**(**' *type-name* '**)**' ) |
    '**\***'

argument-name is any valid C++ identifier.
default-value is any valid C++ expression; if necessary, user code can compute it in terms of previous-name ## _type, where previous-name is the argument-name in a previous specifier-group0 or specifier-group1. This expression will be invoked exactly once.
mfc is an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|, and whose return type is a Boolean Integral Constant; however, user code cannot compute mfc in terms of previous-name ## _type.
type-name is either the name of a target type or an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|_, and whose return type is the target type. If restriction uses this form, then the type of the generated name argument-name ## _type will be computed in terms of the target type, and the generated reference argument-name (but not its corresponding entry in args) will be cast to that type.

Approximate expansion:

Where:

n denotes the minimum arity, as determined from arguments.
m denotes the maximum arity, as determined from arguments.

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename Args>
using boost_param_result\_ ## __LINE__ ## **name** = **result**;

// If **result** is a simple return type:
template <typename Args>
struct boost_param_result\_ ## __LINE__ ## **name**
{
    typedef **result** type;
};

struct boost_param_params\_ ## __LINE__ ## **name**
  : |parameters|_\<
        *list of parameter specifications, based on arguments*
    >
{
};

typedef boost_param_params\_ ## __LINE__ ## **name**
    boost_param_parameters\_ ## __LINE__ ## **name**;

template <typename A0, …, typename A ## **n**>
**result** **name**\ (
    A0&& a0, …, A ## **n**\ && a ## **n**
  , typename boost_param_parameters\_ ## __LINE__ ## **name**
    ::match<A0, …, A ## **n**>::type
    = boost_param_parameters\_ ## __LINE__ ## **name**\ ()
)
{
    return this->boost_param_impl ## __LINE__ ## **name**\ (
        boost_param_parameters\_ ## __LINE__ ## **name**\ ()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **n**>(a ## **n**)
        )
    );
}

:vellipsis:`⋮`

template <typename A0, …, typename A ## **m**>
**result** **name**\ (
    A0&& a0, …, A ## **m**\ && a ## **m**
  , typename boost_param_parameters\_ ## __LINE__ ## **name**
    ::match<A0, …, A ## **m**>::type
    = boost_param_parameters\_ ## __LINE__ ## **name**\ ()
)
{
    return this->boost_param_impl ## __LINE__ ## **name**\ (
        boost_param_parameters\_ ## __LINE__ ## **name**\ ()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **m**>(a ## **m**)
        )
    );
}

template <typename Args>
typename boost_param_result\_ ## __LINE__ ## **name**\ <Args>::type
    boost_param_impl ## __LINE__ ## **name**\ (Args const& args)
{
    return this->boost_param_dispatch_0boost\_ ## __LINE__ ## **name**\ (
        static_cast<
            typename boost_param_result\_ ## __LINE__ ## **name**\ <
                Args
            >::type(*)()
        >(|std_nullptr|_\)
      , args
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of required parameter* ## **0**
            >::type
        >(args[ *keyword object of required parameter* ## **0**])
      , …
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of required parameter* ## **n**
            >::type
        >(args[ *keyword object of required parameter* ## **n**])
    );
}

template <
    typename ResultType
  , typename Args
  , typename *argument name* ## **0** ## _type
  , …
  , typename *argument name* ## **n** ## _type
>
ResultType
    boost_param_dispatch_0boost\_ ## __LINE__ ## **name**\ (
        (ResultType(*)())
      , Args const& args
      , *argument name* ## **0** ## _type&& *argument name* ## **0**
      , …
      , *argument name* ## **n** ## _type&& *argument name* ## **n**
    )
{
    return this->boost_param_dispatch_0boost\_ ## __LINE__ ## **name**\ (
        static_cast<ResultType(*)()>(|std_nullptr|_\)
      , (args, *keyword object of optional parameter* ## **n + 1** =
            *default value of optional parameter* ## **n + 1**
        )
      , |std_forward|_\<*argument name* ## **0** ## _type>(
            *argument name* ## **0**
        )
      , …
      , |std_forward|_\<*argument name* ## **n** ## _type>(
            *argument name* ## **n**
        )
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of optional parameter* ## **n + 1**
            >::type
        >(*default value of optional parameter* ## **n + 1**)
    );
}

:vellipsis:`⋮`

template <
    typename ResultType
  , typename Args
  , typename *argument name* ## **0** ## _type
  , …
  , typename *argument name* ## **m** ## _type
>
ResultType
    boost_param_dispatch_0boost\_ ## __LINE__ ## **name**\ (
        (ResultType(*)())
      , Args const& args
      , *argument name* ## **0** ## _type&& *argument name* ## **0**
      , …
      , *argument name* ## **m** ## _type&& *argument name* ## **m**
    )

.. |BOOST_PARAMETER_CONST_MEMBER_FUNCTION| replace:: BOOST_PARAMETER_CONST_MEMBER_FUNCTION .. _BOOST_PARAMETER_CONST_MEMBER_FUNCTION:

`BOOST_PARAMETER_CONST_MEMBER_FUNCTION(result, name, tag_ns, arguments)`

:Defined in: |preprocessor_header|_

Generates a member function that can take in positional arguments, composed arguments, named arguments, and deduced arguments.

:Example usage:

The return type of each of the following function templates falls under a different value category.

.. parsed-literal::

template <std::size_t N>
|std_bitset|_\<N + 1> rvalue_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1> const rvalue_const_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1>& lvalue_bitset()
{
    static |std_bitset|_\<N + 1> lset = |std_bitset|_\<N + 1>();
    return lset;
}

template <std::size_t N>
|std_bitset|_\<N + 1> const& lvalue_const_bitset()
{
    static |std_bitset|_\<N + 1> const clset = |std_bitset|_\<N + 1>();
    return clset;
}

.. parsed-literal::

enum invoked
{
    passed_by_lvalue_reference_to_const
  , passed_by_lvalue_reference
  , passed_by_rvalue_reference_to_const
  , passed_by_rvalue_reference
};

struct U
{
    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&)
    {
        return passed_by_lvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&)
    {
        return passed_by_lvalue_reference;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&&)
    {
        return passed_by_rvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&&)
    {
        return passed_by_rvalue_reference;
    }
};

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\((_lrc, kw) in(lrc))
|BOOST_PARAMETER_NAME|_\((_lr, kw) in_out(lr))
|BOOST_PARAMETER_NAME|_\((_rrc, kw) in(rrc))
|BOOST_PARAMETER_NAME|_\((_rr, kw) consume(rr))

Use the macro as a substitute for a normal const member function header. Enclose the return type bool in parentheses. For each parameter, also enclose the expected value type in parentheses. Since the value types are mutually exclusive, you can wrap the parameters in a (deduced …) clause. Otherwise, just as with a normal function, the order in which you specify the parameters determines their position. Also, just as with a normal function, optional parameters have default values, whereas required parameters do not. Within the function body, either simply use the parameter name or pass the matching identifier with the leading underscore to the bracket operator of args to extract the corresponding argument. Note that the second method doesn't require std::forward to preserve value categories.

.. parsed-literal::

struct B
{
    B()
    {
    }

    BOOST_PARAMETER_CONST_MEMBER_FUNCTION((bool), evaluate, kw,
        (deduced
            (required
                (lrc, (|std_bitset|_\<1>))
                (lr, (|std_bitset|_\<2>))
            )
            (optional
                (rrc, (|std_bitset|_\<3>), rvalue_const_bitset<2>())
                (rr, (|std_bitset|_\<4>), rvalue_bitset<3>())
            )
        )
    )
    {
        BOOST_TEST_EQ(
            passed_by_lvalue_reference_to_const
          , U::evaluate_category<0>(lrc)
        );
        BOOST_TEST_EQ(
            passed_by_lvalue_reference
          , U::evaluate_category<1>(lr)
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference_to_const
          , U::evaluate_category<2>(|std_forward|_\<rrc0_type>(rrc0))
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference
          , U::evaluate_category<3>(args[_rr0])
        );

        return true;
    }
};

The following function calls are legal.

.. parsed-literal::

B const b = B();
b.evaluate(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
  , rvalue_bitset<3>()
);
b.evaluate(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
);
b.evaluate((  // composed arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
));
b.evaluate(  // named arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
);
b.evaluate(  // named arguments
    _lr0 = lvalue_bitset<1>()
  , _lrc0 = lvalue_const_bitset<0>()
);

Because the parameters were wrapped in a (deduced …) clause, the following function calls are also legal.

.. parsed-literal::

b.evaluate(  // deduced arguments
    rvalue_bitset<3>()
  , lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
);
b.evaluate(  // deduced arguments
    lvalue_bitset<1>()
  , lvalue_const_bitset<0>()
);

The |preprocessor_cpp|_ test program demonstrates proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function.
name is the base name of the function; it determines the name of the generated forwarding functions.
tag_namespace is the namespace in which the keywords used by the function resides.
arguments is a |Boost_Preprocessor|_ sequence_ of argument-specifiers, as defined below.

Argument specifiers syntax:

.. parsed-literal::

argument-specifiers ::= *specifier-group0* {*specifier-group0*\ }

specifier-group0 ::= *specifier-group1* |
    (
        '**(**' '**deduced**'
            *specifier-group1* {*specifier-group1*\ }
        '**)**'
    )

specifier-group1 ::=
    (
        '**(**' '**optional**'
            *optional-specifier* {*optional-specifier*\ }
        '**)**'
    ) | (
        '**(**' '**required**'
            *required-specifier* {*required-specifier*\ }
        '**)**'
    )

optional-specifier ::=
    '**(**'
        *argument-name* '**,**' *restriction* '**,**' *default-value*
    ')'

required-specifier ::=
    '**(**' *argument-name* '**,**' *restriction* ')'

restriction ::=
    ( '**\***' '**(**' *mfc* '**)**' ) |
    ( '**(**' *type-name* '**)**' ) |
    '**\***'

argument-name is any valid C++ identifier.
default-value is any valid C++ expression; if necessary, user code can compute it in terms of previous-name ## _type, where previous-name is the argument-name in a previous specifier-group0 or specifier-group1. This expression will be invoked exactly once.
mfc is an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|, and whose return type is a Boolean Integral Constant; however, user code cannot compute mfc in terms of previous-name ## _type.
type-name is either the name of a target type or an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|_, and whose return type is the target type. If restriction uses this form, then the type of the generated name argument-name ## _type will be computed in terms of the target type, and the generated reference argument-name (but not its corresponding entry in args) will be cast to that type.

Approximate expansion:

Where:

n denotes the minimum arity, as determined from arguments.
m denotes the maximum arity, as determined from arguments.

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename Args>
using boost_param_result_const\_ ## __LINE__ ## **name** = **result**;

// If **result** is a simple return type:
template <typename Args>
struct boost_param_result_const\_ ## __LINE__ ## **name**
{
    typedef **result** type;
};

struct boost_param_params_const\_ ## __LINE__ ## **name**
  : |parameters|_\<
        *list of parameter specifications, based on arguments*
    >
{
};

typedef boost_param_params_const\_ ## __LINE__ ## **name**
    boost_param_parameters_const\_ ## __LINE__ ## **name**;

template <typename A0, …, typename A ## **n**>
**result** **name**\ (
    A0&& a0, …, A ## **n**\ && a ## **n**
  , typename boost_param_parameters_const\_ ## __LINE__ ## **name**
    ::match<A0, …, A ## **n**>::type
    = boost_param_parameters_const\_ ## __LINE__ ## **name**\ ()
) const
{
    return this->boost_param_impl_const ## __LINE__ ## **name**\ (
        boost_param_parameters_const\_ ## __LINE__ ## **name**\ (
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **n**>(a ## **n**)
        )
    );
}

:vellipsis:`⋮`

template <typename A0, …, typename A ## **m**>
**result** **name**\ (
    A0&& a0, …, A ## **m**\ && a ## **m**
  , typename boost_param_parameters_const\_ ## __LINE__ ## **name**
    ::match<A0, …, A ## **m**>::type
    = boost_param_parameters_const\_ ## __LINE__ ## **name**\ ()
) const
{
    return this->boost_param_impl_const ## __LINE__ ## **name**\ (
        boost_param_parameters_const\_ ## __LINE__ ## **name**\ ()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **m**>(a ## **m**)
        )
    );
}

template <typename Args>
typename boost_param_result_const\_ ## __LINE__ ## **name**\ <Args>::type
    boost_param_impl_const ## __LINE__ ## **name**\ (Args const& args) const
{
    return this->
    boost_param_dispatch_const_0boost\_ ## __LINE__ ## **name**\ (
        static_cast<
            typename boost_param_result_const\_ ## __LINE__ ## **name**\ <
                Args
            >::type(*)()
        >(|std_nullptr|_\)
      , args
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of required parameter* ## **0**
            >::type
        >(args[ *keyword object of required parameter* ## **0**])
      , …
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of required parameter* ## **n**
            >::type
        >(args[ *keyword object of required parameter* ## **n**])
    );
}

template <
    typename ResultType
  , typename Args
  , typename *argument name* ## **0** ## _type
  , …
  , typename *argument name* ## **n** ## _type
>
ResultType
    boost_param_dispatch_const_0boost\_ ## __LINE__ ## **name**\ (
        (ResultType(*)())
      , Args const& args
      , *argument name* ## **0** ## _type&& *argument name* ## **0**
      , …
      , *argument name* ## **n** ## _type&& *argument name* ## **n**
    ) const
{
    return this->
    boost_param_dispatch_const_0boost\_ ## __LINE__ ## **name**\ (
        static_cast<ResultType(*)()>(|std_nullptr|_\)
      , (args, *keyword object of optional parameter* ## **n + 1** =
            *default value of optional parameter* ## **n + 1**
        )
      , |std_forward|_\<*argument name* ## **0** ## _type>(
            *argument name* ## **0**
        )
      , …
      , |std_forward|_\<*argument name* ## **n** ## _type>(
            *argument name* ## **n**
        )
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of optional parameter* ## **n + 1**
            >::type
        >(*default value of optional parameter* ## **n + 1**)
    );
}

:vellipsis:`⋮`

template <
    typename ResultType
  , typename Args
  , typename *argument name* ## **0** ## _type
  , …
  , typename *argument name* ## **m** ## _type
>
ResultType
    boost_param_dispatch_const_0boost\_ ## __LINE__ ## **name**\ (
        (ResultType(*)())
      , Args const& args
      , *argument name* ## **0** ## _type&& *argument name* ## **0**
      , …
      , *argument name* ## **m** ## _type&& *argument name* ## **m**
    ) const

.. |BOOST_PARAMETER_FUNCTION_CALL_OPERATOR| replace:: BOOST_PARAMETER_FUNCTION_CALL_OPERATOR .. _BOOST_PARAMETER_FUNCTION_CALL_OPERATOR:

`BOOST_PARAMETER_FUNCTION_CALL_OPERATOR(result, tag_namespace, arguments)`

:Defined in: |preprocessor_header|_

Generates a function call operator that can take in positional arguments, composed arguments, named arguments, and deduced arguments.

:Example usage:

Define the named parameters that will comprise the argument specification that this macro will use. Ensure that all their tag types are in the same namespace, which is tag by default.

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\(y)
|BOOST_PARAMETER_NAME|_\(z)

Use the macro as a substitute for a normal function call operator header. Enclose the return type in parentheses. For each parameter, also enclose the expected value type in parentheses. Since the value types are mutually exclusive, you can wrap the parameters in a (deduced …) clause. This is especially useful when implementing multiple Boost.Parameter-enabled function call operator overloads.

.. parsed-literal::

class char_reader
{
    int index;
    char const* key;

 public:
    explicit char_reader(char const* k) : index(0), key(k)
    {
    }

    BOOST_PARAMETER_FUNCTION_CALL_OPERATOR((void), tag,
        (deduced
            (required
                (y, (int))
                (z, (char const*))
            )
        )
    )
    {
        this->index = y;
        this->key = z;
    }

    |BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR|_\((char), tag,
        (deduced
            (required
                (y, (bool))
                (z, (|std_map|_\<char const*, |std_string|_\>))
            )
        )
    )
    {
        return y ? (
            (z.find(this->key)->second)[this->index]
        ) : this->key[this->index];
    }
};

As with regular argument-dependent lookup, the value types of the arguments passed in determine which function call operator overload gets invoked.

.. parsed-literal::

char const* keys[] = {"foo", "bar", "baz"};
|std_map|_\<char const*, |std_string|_\> k2s;
k2s[keys[0]] = |std_string|_\("qux");
k2s[keys[1]] = |std_string|_\("wmb");
k2s[keys[2]] = |std_string|_\("zxc");
char_reader r(keys[0]);

// positional arguments
BOOST_TEST_EQ('q', (r(true, k2s)));
BOOST_TEST_EQ('f', (r(false, k2s)));

// named arguments
r(_z = keys[1], _y = 1);
BOOST_TEST_EQ('m', (r(_z = k2s, _y = true)));
BOOST_TEST_EQ('a', (r(_z = k2s, _y = false)));

// deduced arguments
r(keys[2], 2);
BOOST_TEST_EQ('c', (r(k2s, true)));
BOOST_TEST_EQ('z', (r(k2s, false)));

The |preprocessor_cpp|_ and |preprocessor_deduced_cpp|_ test programs demonstrate proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function call operator.
tag_namespace is the namespace in which the keywords used by the function call operator resides.
arguments is a |Boost_Preprocessor|_ sequence_ of argument-specifiers, as defined below.

Argument specifiers syntax:

.. parsed-literal::

argument-specifiers ::= *specifier-group0* {*specifier-group0*\ }

specifier-group0 ::= *specifier-group1* |
    (
        '**(**' '**deduced**'
            *specifier-group1* {*specifier-group1*\ }
        '**)**'
    )

specifier-group1 ::=
    (
        '**(**' '**optional**'
            *optional-specifier* {*optional-specifier*\ }
        '**)**'
    ) | (
        '**(**' '**required**'
            *required-specifier* {*required-specifier*\ }
        '**)**'
    )

optional-specifier ::=
    '**(**'
        *argument-name* '**,**' *restriction* '**,**' *default-value*
    ')'

required-specifier ::=
    '**(**' *argument-name* '**,**' *restriction* ')'

restriction ::=
    ( '**\***' '**(**' *mfc* '**)**' ) |
    ( '**(**' *type-name* '**)**' ) |
    '**\***'

argument-name is any valid C++ identifier.
default-value is any valid C++ expression; if necessary, user code can compute it in terms of previous-name ## _type, where previous-name is the argument-name in a previous specifier-group0 or specifier-group1. This expression will be invoked exactly once.
mfc is an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|, and whose return type is a Boolean Integral Constant; however, user code cannot compute mfc in terms of previous-name ## _type.
type-name is either the name of a target type or an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|_, and whose return type is the target type. If restriction uses this form, then the type of the generated name argument-name ## _type will be computed in terms of the target type, and the generated reference argument-name (but not its corresponding entry in args) will be cast to that type.

Approximate expansion:

Where:

n denotes the minimum arity, as determined from arguments.
m denotes the maximum arity, as determined from arguments.

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename Args>
using boost_param_result\_ ## __LINE__ ## operator = **result**;

// If **result** is a simple return type:
template <typename Args>
struct boost_param_result\_ ## __LINE__ ## operator
{
    typedef **result** type;
};

struct boost_param_params\_ ## __LINE__ ## operator
  : |parameters|_\<
        *list of parameter specifications, based on arguments*
    >
{
};

typedef boost_param_params\_ ## __LINE__ ## operator
    boost_param_parameters\_ ## __LINE__ ## operator;

template <typename A0, …, typename A ## **n**>
**result** operator()(
    A0&& a0, …, A ## **n**\ && a ## **n**
  , typename boost_param_parameters\_ ## __LINE__ ## operator::match<
        A0, …, A ## **n**
    >::type = boost_param_parameters\_ ## __LINE__ ## operator()
)
{
    return this->boost_param_impl ## __LINE__ ## operator(
        boost_param_parameters\_ ## __LINE__ ## operator()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **n**>(a ## **n**)
        )
    );
}

:vellipsis:`⋮`

template <typename A0, …, typename A ## **m**>
**result** operator()(
    A0&& a0, …, A ## **m**\ && a ## **m**
  , typename boost_param_parameters\_ ## __LINE__ ## operator::match<
        A0, …, A ## **m**
    >::type = boost_param_parameters\_ ## __LINE__ ## operator()
)
{
    return this->boost_param_impl ## __LINE__ ## operator(
        boost_param_parameters\_ ## __LINE__ ## operator()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **m**>(a ## **m**)
        )
    );
}

template <typename Args>
typename boost_param_result\_ ## __LINE__ ## operator<Args>::type
    boost_param_impl ## __LINE__ ## operator(Args const& args)
{
    return this->boost_param_dispatch_0boost\_ ## __LINE__ ## operator(
        static_cast<
            typename boost_param_result\_ ## __LINE__ ## operator<
                Args
            >::type(*)()
        >(|std_nullptr|_\)
      , args
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of required parameter* ## **0**
            >::type
        >(args[ *keyword object of required parameter* ## **0**])
      , …
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of required parameter* ## **n**
            >::type
        >(args[ *keyword object of required parameter* ## **n**])
    );
}

template <
    typename ResultType
  , typename Args
  , typename *argument name* ## **0** ## _type
  , …
  , typename *argument name* ## **n** ## _type
>
ResultType
    boost_param_dispatch_0boost\_ ## __LINE__ ## operator(
        (ResultType(*)())
      , Args const& args
      , *argument name* ## **0** ## _type&& *argument name* ## **0**
      , …
      , *argument name* ## **n** ## _type&& *argument name* ## **n**
    )
{
    return this->boost_param_dispatch_0boost\_ ## __LINE__ ## operator(
        static_cast<ResultType(*)()>(|std_nullptr|_\)
      , (args, *keyword object of optional parameter* ## **n + 1** =
            *default value of optional parameter* ## **n + 1**
        )
      , |std_forward|_\<*argument name* ## **0** ## _type>(
            *argument name* ## **0**
        )
      , …
      , |std_forward|_\<*argument name* ## **n** ## _type>(
            *argument name* ## **n**
        )
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of optional parameter* ## **n + 1**
            >::type
        >(*default value of optional parameter* ## **n + 1**)
    );
}

:vellipsis:`⋮`

template <
    typename ResultType
  , typename Args
  , typename *argument name* ## **0** ## _type
  , …
  , typename *argument name* ## **m** ## _type
>
ResultType
    boost_param_dispatch_0boost\_ ## __LINE__ ## operator(
        (ResultType(*)())
      , Args const& args
      , *argument name* ## **0** ## _type&& *argument name* ## **0**
      , …
      , *argument name* ## **m** ## _type&& *argument name* ## **m**
    )

.. |BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR| replace:: BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR .. _BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR:

`BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR(result, tag_ns, arguments)`

:Defined in: |preprocessor_header|_

Generates a function call operator that can take in positional arguments, composed arguments, named arguments, and deduced arguments.

:Example usage:

The return type of each of the following function templates falls under a different value category.

.. parsed-literal::

template <std::size_t N>
|std_bitset|_\<N + 1> rvalue_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1> const rvalue_const_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1>& lvalue_bitset()
{
    static |std_bitset|_\<N + 1> lset = |std_bitset|_\<N + 1>();
    return lset;
}

template <std::size_t N>
|std_bitset|_\<N + 1> const& lvalue_const_bitset()
{
    static |std_bitset|_\<N + 1> const clset = |std_bitset|_\<N + 1>();
    return clset;
}

.. parsed-literal::

enum invoked
{
    passed_by_lvalue_reference_to_const
  , passed_by_lvalue_reference
  , passed_by_rvalue_reference_to_const
  , passed_by_rvalue_reference
};

struct U
{
    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&)
    {
        return passed_by_lvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&)
    {
        return passed_by_lvalue_reference;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&&)
    {
        return passed_by_rvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&&)
    {
        return passed_by_rvalue_reference;
    }
};

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\((_lrc, kw) in(lrc))
|BOOST_PARAMETER_NAME|_\((_lr, kw) in_out(lr))
|BOOST_PARAMETER_NAME|_\((_rrc, kw) in(rrc))
|BOOST_PARAMETER_NAME|_\((_rr, kw) consume(rr))

Use the macro as a substitute for a normal const function call operator header. Enclose the return type bool in parentheses. For each parameter, also enclose the expected value type in parentheses. Since the value types are mutually exclusive, you can wrap the parameters in a (deduced …) clause. Otherwise, just as with a normal function, the order in which you specify the parameters determines their position. Also, just as with a normal function, optional parameters have default values, whereas required parameters do not. Within the function body, either simply use the parameter name or pass the matching identifier with the leading underscore to the bracket operator of args to extract the corresponding argument. Note that the second method doesn't require std::forward to preserve value categories.

.. parsed-literal::

struct B
{
    B()
    {
    }

    BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR((bool), kw,
        (deduced
            (required
                (lrc, (|std_bitset|_\<1>))
                (lr, (|std_bitset|_\<2>))
            )
            (optional
                (rrc, (|std_bitset|_\<3>), rvalue_const_bitset<2>())
                (rr, (|std_bitset|_\<4>), rvalue_bitset<3>())
            )
        )
    )
    {
        BOOST_TEST_EQ(
            passed_by_lvalue_reference_to_const
          , U::evaluate_category<0>(lrc)
        );
        BOOST_TEST_EQ(
            passed_by_lvalue_reference
          , U::evaluate_category<1>(lr)
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference_to_const
          , U::evaluate_category<2>(|std_forward|_\<rrc0_type>(rrc0))
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference
          , U::evaluate_category<3>(args[_rr0])
        );

        return true;
    }
};

The following function calls are legal.

.. parsed-literal::

B const b = B();
b(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
  , rvalue_bitset<3>()
);
b(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
);
b((  // composed arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
));
b(  // named arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
);
b(  // named arguments
    _lr0 = lvalue_bitset<1>()
  , _lrc0 = lvalue_const_bitset<0>()
);

Because the parameters were wrapped in a (deduced …) clause, the following function calls are also legal.

.. parsed-literal::

b(  // deduced arguments
    rvalue_bitset<3>()
  , lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
);
b(  // deduced arguments
    lvalue_bitset<1>()
  , lvalue_const_bitset<0>()
);

The |preprocessor_cpp|, |preprocessor_deduced_cpp|, and |preprocessor_eval_cat_8_cpp|_ test programs demonstrate proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function call operator.
tag_namespace is the namespace in which the keywords used by the function call operator resides.
arguments is a |Boost_Preprocessor|_ sequence_ of argument-specifiers, as defined below.

Argument specifiers syntax:

.. parsed-literal::

argument-specifiers ::= *specifier-group0* {*specifier-group0*\ }

specifier-group0 ::= *specifier-group1* |
    (
        '**(**' '**deduced**'
            *specifier-group1* {*specifier-group1*\ }
        '**)**'
    )

specifier-group1 ::=
    (
        '**(**' '**optional**'
            *optional-specifier* {*optional-specifier*\ }
        '**)**'
    ) | (
        '**(**' '**required**'
            *required-specifier* {*required-specifier*\ }
        '**)**'
    )

optional-specifier ::=
    '**(**'
        *argument-name* '**,**' *restriction* '**,**' *default-value*
    ')'

required-specifier ::=
    '**(**' *argument-name* '**,**' *restriction* ')'

restriction ::=
    ( '**\***' '**(**' *mfc* '**)**' ) |
    ( '**(**' *type-name* '**)**' ) |
    '**\***'

argument-name is any valid C++ identifier.
default-value is any valid C++ expression; if necessary, user code can compute it in terms of previous-name ## _type, where previous-name is the argument-name in a previous specifier-group0 or specifier-group1. This expression will be invoked exactly once.
mfc is an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|, and whose return type is a Boolean Integral Constant; however, user code cannot compute mfc in terms of previous-name ## _type.
type-name is either the name of a target type or an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|_, and whose return type is the target type. If restriction uses this form, then the type of the generated name argument-name ## _type will be computed in terms of the target type, and the generated reference argument-name (but not its corresponding entry in args) will be cast to that type.

Approximate expansion:

Where:

n denotes the minimum arity, as determined from arguments.
m denotes the maximum arity, as determined from arguments.

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename Args>
using boost_param_result_const\_ ## __LINE__ ## operator = **result**;

// If **result** is a simple return type:
template <typename Args>
struct boost_param_result_const\_ ## __LINE__ ## operator
{
    typedef **result** type;
};

struct boost_param_params_const\_ ## __LINE__ ## operator
  : |parameters|_\<
        *list of parameter specifications, based on arguments*
    >
{
};

typedef boost_param_params_const\_ ## __LINE__ ## operator
    boost_param_parameters_const\_ ## __LINE__ ## operator;

template <typename A0, …, typename A ## **n**>
**result** operator()(
    A0&& a0, …, A ## **n**\ && a ## **n**
  , typename boost_param_parameters_const\_ ## __LINE__ ## operator
    ::match<A0, …, A ## **n**>::type
    = boost_param_parameters_const\_ ## __LINE__ ## operator()
) const
{
    return this->boost_param_impl_const ## __LINE__ ## operator(
        boost_param_parameters_const\_ ## __LINE__ ## operator()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **n**>(a ## **n**)
        )
    );
}

:vellipsis:`⋮`

template <typename A0, …, typename A ## **m**>
**result** operator()(
    A0&& a0, …, A ## **m**\ && a ## **m**
  , typename boost_param_parameters_const\_ ## __LINE__ ## operator
    ::match<A0, …, A ## **m**>::type
    = boost_param_parameters_const\_ ## __LINE__ ## operator()
) const
{
    return this->boost_param_impl_const ## __LINE__ ## operator(
        boost_param_parameters_const\_ ## __LINE__ ## operator()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **m**>(a ## **m**)
        )
    );
}

template <typename Args>
typename boost_param_result_const\_ ## __LINE__ ## operator<Args>::type
    boost_param_impl_const ## __LINE__ ## operator(Args const& args) const
{
    return this->
    boost_param_dispatch_const_0boost\_ ## __LINE__ ## operator(
        static_cast<
            typename boost_param_result_const\_ ## __LINE__ ## operator<
                Args
            >::type(*)()
        >(|std_nullptr|_\)
      , args
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of required parameter* ## **0**
            >::type
        >(args[ *keyword object of required parameter* ## **0**])
      , …
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of required parameter* ## **n**
            >::type
        >(args[ *keyword object of required parameter* ## **n**])
    );
}

template <
    typename ResultType
  , typename Args
  , typename *argument name* ## **0** ## _type
  , …
  , typename *argument name* ## **n** ## _type
>
ResultType
    boost_param_dispatch_const_0boost\_ ## __LINE__ ## operator(
        (ResultType(*)())
      , Args const& args
      , *argument name* ## **0** ## _type&& *argument name* ## **0**
      , …
      , *argument name* ## **n** ## _type&& *argument name* ## **n**
    ) const
{
    return this->
    boost_param_dispatch_const_0boost\_ ## __LINE__ ## operator(
        static_cast<ResultType(*)()>(|std_nullptr|_\)
      , (args, *keyword object of optional parameter* ## **n + 1** =
            *default value of optional parameter* ## **n + 1**
        )
      , |std_forward|_\<*argument name* ## **0** ## _type>(
            *argument name* ## **0**
        )
      , …
      , |std_forward|_\<*argument name* ## **n** ## _type>(
            *argument name* ## **n**
        )
      , |std_forward|_\<
            typename |value_type|_\<
                Args
              , *keyword tag type of optional parameter* ## **n + 1**
            >::type
        >(*default value of optional parameter* ## **n + 1**)
    );
}

:vellipsis:`⋮`

template <
    typename ResultType
  , typename Args
  , typename *argument name* ## **0** ## _type
  , …
  , typename *argument name* ## **m** ## _type
>
ResultType
    boost_param_dispatch_const_0boost\_ ## __LINE__ ## operator(
        (ResultType(*)())
      , Args const& args
      , *argument name* ## **0** ## _type&& *argument name* ## **0**
      , …
      , *argument name* ## **m** ## _type&& *argument name* ## **m**
    ) const

.. |BOOST_PARAMETER_CONSTRUCTOR| replace:: BOOST_PARAMETER_CONSTRUCTOR .. _BOOST_PARAMETER_CONSTRUCTOR:

`BOOST_PARAMETER_CONSTRUCTOR(cls, impl, tag_namespace, arguments)`

:Defined in: |preprocessor_header|_

Generates a constructor that can take in positional arguments, composed arguments, named arguments, and deduced arguments.

:Example usage:

Define the named parameters that will comprise the argument specification that this macro will use. Ensure that all their tag types are in the same namespace, which is tag by default.

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\(y)
|BOOST_PARAMETER_NAME|_\(z)

In the base class, implement a delegate constructor template that takes in an |ArgumentPack|_. You must pass the identifiers with leading underscores to args in order to extract the corresponding arguments.

.. parsed-literal::

class char_read_base
{
    int index;
    char const* key;

 public:
    template <typename Args>
    explicit char_read_base(Args const& args)
      : index(args[_y]), key(args[_z])
    {
    }

    |BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR|_\((char), tag,
        (deduced
            (required
                (y, (bool))
                (z, (|std_map|_\<char const*, |std_string|_\>))
            )
        )
    )
    {
        return y ? (
            (z.find(this->key)->second)[this->index]
        ) : this->key[this->index];
    }
};

Use the macro as a substitute for a normal constructor definition. Note the lack of an explicit body. Enclose the base type in parentheses. For each parameter, also enclose the expected value type in parentheses. Since the value types are mutually exclusive, you can wrap the parameters in a (deduced …) clause.

.. parsed-literal::

struct char_reader : public char_read_base
{
    BOOST_PARAMETER_CONSTRUCTOR(char_reader, (char_read_base), tag,
        (deduced
            (required
                (y, (int))
                (z, (char const*))
            )
        )
    )
};

The following char_reader constructor calls are legal.

.. parsed-literal::

char const* keys[] = {"foo", "bar", "baz"};
|std_map|_\<char const*, |std_string|_\> k2s;
k2s[keys[0]] = |std_string|_\("qux");
k2s[keys[1]] = |std_string|_\("wmb");
k2s[keys[2]] = |std_string|_\("zxc");

// positional arguments
char_reader r0(0, keys[0]);
BOOST_TEST_EQ('q', (r0(true, k2s)));
BOOST_TEST_EQ('f', (r0(false, k2s)));

// named arguments
char_reader r1(_z = keys[1], _y = 1);
BOOST_TEST_EQ('m', (r1(_z = k2s, _y = true)));
BOOST_TEST_EQ('a', (r1(_z = k2s, _y = false)));

// deduced arguments
char_reader r2(keys[2], 2);
BOOST_TEST_EQ('c', (r2(k2s, true)));
BOOST_TEST_EQ('z', (r2(k2s, false)));

The |preprocessor_cpp|_ and |preprocessor_deduced_cpp|_ test programs demonstrate proper usage of this macro.

Macro parameters:

cls is the name of the enclosing class.
impl is the parenthesized implementation base class for cls.
tag_namespace is the namespace in which the keywords used by the constructor resides.
arguments is a list of argument-specifiers, as defined below.

Argument specifiers syntax:

.. parsed-literal::

argument-specifiers ::= *specifier-group0* {*specifier-group0*\ }

specifier-group0 ::= *specifier-group1* |
    (
        '**(**' '**deduced**'
            *specifier-group1* {*specifier-group1*\ }
        '**)**'
    )

specifier-group1 ::=
    (
        '**(**' '**optional**'
            *specifier* {*specifier*\ }
        '**)**'
    ) | (
        '**(**' '**required**'
            *specifier* {*specifier*\ }
        '**)**'
    )

specifier ::=
    '**(**' *argument-name* '**,**' *restriction* ')'

restriction ::=
    ( '**\***' '**(**' *mfc* '**)**' ) |
    ( '**(**' *type-name* '**)**' ) |
    '**\***'

argument-name is any valid C++ identifier.
mfc is an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|, and whose return type is a Boolean Integral Constant; however, user code cannot compute mfc in terms of previous-name ## _type.
type-name is either the name of a target type or an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|_, and whose return type is the target type.

Note that specifier does not include default-value. It is up to the delegate constructor in impl to determine the default value of all optional arguments.

Approximate expansion:

Where:

n denotes the minimum arity, as determined from arguments.
m denotes the maximum arity, as determined from arguments.

.. parsed-literal::

struct boost_param_params\_ ## __LINE__ ## ctor
  : |parameters|_\<
        *list of parameter specifications, based on arguments*
    >
{
};

typedef boost_param_params\_ ## __LINE__ ## ctor
    constructor_parameters ## __LINE__;

template <typename A0, …, typename A ## **n**>
**cls**\ (A0&& a0, …, A ## **n** && a ## **n**)
  : **impl**\ (
        constructor_parameters ## __LINE__(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **n**>(a ## **n**)
        )
    )
{
}

:vellipsis:`⋮`

template <typename A0, …, typename A ## **m**>
**cls**\ (A0&& a0, …, A ## **m** && a ## **m**)
  : **impl**\ (
        constructor_parameters ## __LINE__(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **m**>(a ## **m**)
        )
    )
{
}

.. |BOOST_PARAMETER_BASIC_FUNCTION| replace:: BOOST_PARAMETER_BASIC_FUNCTION .. _BOOST_PARAMETER_BASIC_FUNCTION:

`BOOST_PARAMETER_BASIC_FUNCTION(result, name, tag_namespace, arguments)`

:Defined in: |preprocessor_header|_

Generates a function that can take in positional arguments, composed arguments, named arguments, and deduced arguments.

:Example usage:

The return type of each of the following function templates falls under a different value category.

.. parsed-literal::

template <std::size_t N>
|std_bitset|_\<N + 1> rvalue_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1> const rvalue_const_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1>& lvalue_bitset()
{
    static |std_bitset|_\<N + 1> lset = |std_bitset|_\<N + 1>();
    return lset;
}

template <std::size_t N>
|std_bitset|_\<N + 1> const& lvalue_const_bitset()
{
    static |std_bitset|_\<N + 1> const clset = |std_bitset|_\<N + 1>();
    return clset;
}

.. parsed-literal::

enum invoked
{
    passed_by_lvalue_reference_to_const
  , passed_by_lvalue_reference
  , passed_by_rvalue_reference_to_const
  , passed_by_rvalue_reference
};

struct U
{
    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&)
    {
        return passed_by_lvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&)
    {
        return passed_by_lvalue_reference;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&&)
    {
        return passed_by_rvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&&)
    {
        return passed_by_rvalue_reference;
    }
};

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\((_lrc, kw) in(lrc))
|BOOST_PARAMETER_NAME|_\((_lr, kw) in_out(lr))
|BOOST_PARAMETER_NAME|_\((_rrc, kw) in(rrc))
|BOOST_PARAMETER_NAME|_\((_rr, kw) consume(rr))

Use the macro as a substitute for a normal function header. Enclose the return type bool in parentheses. For each parameter, also enclose the expected value type in parentheses. Since the value types are mutually exclusive, you can wrap the parameters in a (deduced …) clause. Otherwise, just as with a normal function, the order in which you specify the parameters determines their position. However, unlike a normal function, default values must be specified within the function body. Also within the function body, you must pass the matching identifier with the leading underscore to the bracket operator of args to extract the corresponding argument, but at least this doesn't require std::forward to preserve value categories.

.. parsed-literal::

BOOST_PARAMETER_BASIC_FUNCTION((bool), evaluate, kw,
    (deduced
        (required
            (lrc, (|std_bitset|_\<1>))
            (lr, (|std_bitset|_\<2>))
        )
        (optional
            (rrc, (|std_bitset|_\<3>))
            (rr, (|std_bitset|_\<4>))
        )
    )
)
{
    BOOST_TEST_EQ(
        passed_by_lvalue_reference_to_const
      , U::evaluate_category<0>(args[_lrc])
    );
    BOOST_TEST_EQ(
        passed_by_lvalue_reference
      , U::evaluate_category<1>(args[_lr])
    );
    BOOST_TEST_EQ(
        passed_by_rvalue_reference_to_const
      , U::evaluate_category<2>(
            args[_rrc0 | rvalue_const_bitset<2>()]
        )
    );
    BOOST_TEST_EQ(
        passed_by_rvalue_reference
      , U::evaluate_category<3>(args[_rr0 | rvalue_bitset<3>()])
    );

    return true;
}

The following function calls are legal.

.. parsed-literal::

evaluate(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
  , rvalue_bitset<3>()
);
evaluate(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
);
evaluate((  // composed arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
));
evaluate(  // named arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
);
evaluate(  // named arguments
    _lr0 = lvalue_bitset<1>()
  , _lrc0 = lvalue_const_bitset<0>()
);

Because the parameters were wrapped in a (deduced …) clause, the following function calls are also legal.

.. parsed-literal::

evaluate(  // deduced arguments
    rvalue_bitset<3>()
  , lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
);
evaluate(  // deduced arguments
    lvalue_bitset<1>()
  , lvalue_const_bitset<0>()
);

The |preprocessor_cpp|_ test program demonstrates proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function.
name is the base name of the function; it determines the name of the generated forwarding functions.
tag_namespace is the namespace in which the keywords used by the function resides.
arguments is a |Boost_Preprocessor|_ sequence_ of argument-specifiers, as defined below.

Argument specifiers syntax:

.. parsed-literal::

argument-specifiers ::= *specifier-group0* {*specifier-group0*\ }

specifier-group0 ::= *specifier-group1* |
    (
        '**(**' '**deduced**'
            *specifier-group1* {*specifier-group1*\ }
        '**)**'
    )

specifier-group1 ::=
    (
        '**(**' '**optional**'
            *specifier* {*specifier*\ }
        '**)**'
    ) | (
        '**(**' '**required**'
            *specifier* {*specifier*\ }
        '**)**'
    )

specifier ::=
    '**(**' *argument-name* '**,**' *restriction* ')'

restriction ::=
    ( '**\***' '**(**' *mfc* '**)**' ) |
    ( '**(**' *type-name* '**)**' ) |
    '**\***'

argument-name is any valid C++ identifier.
mfc is an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|, and whose return type is a Boolean Integral Constant; however, user code cannot compute mfc in terms of previous-name ## _type.
type-name is either the name of a target type or an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|_, and whose return type is the target type.

Note that specifier does not include default-value. It is up to the function body to determine the default value of all optional arguments.

Approximate expansion:

Where:

n denotes the minimum arity, as determined from arguments.
m denotes the maximum arity, as determined from arguments.

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename Args>
using boost_param_result\_ ## __LINE__ ## **name** = **result**;

// If **result** is a simple return type:
template <typename Args>
struct boost_param_result\_ ## __LINE__ ## **name**
{
    typedef **result** type;
};

struct boost_param_params\_ ## __LINE__ ## **name**
  : |parameters|_\<
        *list of parameter specifications, based on arguments*
    >
{
};

typedef boost_param_params\_ ## __LINE__ ## **name**
    boost_param_parameters\_ ## __LINE__ ## **name**;

template <typename Args>
typename boost_param_result\_ ## __LINE__ ## **name**\ <Args>::type
    boost_param_impl ## **name**\ (Args const&);

template <typename A0, …, typename A ## **n**>
**result** **name**\ (
    A0&& a0, …, A ## **n**\ && a ## **n**
  , typename boost_param_parameters\_ ## __LINE__ ## **name**
    ::match<A0, …, A ## **n**>::type
    = boost_param_parameters\_ ## __LINE__ ## **name**\ ()
)
{
    return boost_param_impl ## __LINE__ ## **name**\ (
        boost_param_parameters\_ ## __LINE__ ## **name**\ ()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **n**>(a ## **n**)
        )
    );
}

:vellipsis:`⋮`

template <typename A0, …, typename A ## **m**>
**result** **name**\ (
    A0&& a0, …, A ## **m**\ && a ## **m**
  , typename boost_param_parameters\_ ## __LINE__ ## **name**
    ::match<A0, …, A ## **m**>::type
    = boost_param_parameters\_ ## __LINE__ ## **name**\ ()
)
{
    return boost_param_impl ## __LINE__ ## **name**\ (
        boost_param_parameters\_ ## __LINE__ ## **name**\ ()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **m**>(a ## **m**)
        )
    );
}

template <typename Args>
typename boost_param_result\_ ## __LINE__ ## **name**\ <Args>::type
    boost_param_impl ## __LINE__ ## **name**\ (Args const& args)

Only the |ArgumentPack|_ type Args and its object instance args are available for use within the function body.

.. |BOOST_PARAMETER_BASIC_MEMBER_FUNCTION| replace:: BOOST_PARAMETER_BASIC_MEMBER_FUNCTION .. _BOOST_PARAMETER_BASIC_MEMBER_FUNCTION:

`BOOST_PARAMETER_BASIC_MEMBER_FUNCTION(result, name, tag_ns, arguments)`

:Defined in: |preprocessor_header|_

Generates a member function that can take in positional arguments, composed arguments, named arguments, and deduced arguments.

:Example usage:

The return type of each of the following function templates falls under a different value category.

.. parsed-literal::

template <std::size_t N>
|std_bitset|_\<N + 1> rvalue_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1> const rvalue_const_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1>& lvalue_bitset()
{
    static |std_bitset|_\<N + 1> lset = |std_bitset|_\<N + 1>();
    return lset;
}

template <std::size_t N>
|std_bitset|_\<N + 1> const& lvalue_const_bitset()
{
    static |std_bitset|_\<N + 1> const clset = |std_bitset|_\<N + 1>();
    return clset;
}

.. parsed-literal::

enum invoked
{
    passed_by_lvalue_reference_to_const
  , passed_by_lvalue_reference
  , passed_by_rvalue_reference_to_const
  , passed_by_rvalue_reference
};

struct U
{
    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&)
    {
        return passed_by_lvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&)
    {
        return passed_by_lvalue_reference;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&&)
    {
        return passed_by_rvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&&)
    {
        return passed_by_rvalue_reference;
    }
};

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\((_lrc, kw) in(lrc))
|BOOST_PARAMETER_NAME|_\((_lr, kw) in_out(lr))
|BOOST_PARAMETER_NAME|_\((_rrc, kw) in(rrc))
|BOOST_PARAMETER_NAME|_\((_rr, kw) consume(rr))

Use the macro as a substitute for a normal static member function header. Enclose the return type bool in parentheses. For each parameter, also enclose the expected value type in parentheses. Since the value types are mutually exclusive, you can wrap the parameters in a (deduced …) clause. Otherwise, just as with a normal function, the order in which you specify the parameters determines their position. However, unlike a normal function, default values must be specified within the function body. Also within the function body, you must pass the matching identifier with the leading underscore to the bracket operator of args to extract the corresponding argument, but at least this doesn't require std::forward to preserve value categories.

.. parsed-literal::

struct B
{
    BOOST_PARAMETER_BASIC_MEMBER_FUNCTION((bool), static evaluate, kw,
        (deduced
            (required
                (lrc, (|std_bitset|_\<1>))
                (lr, (|std_bitset|_\<2>))
            )
            (optional
                (rrc, (|std_bitset|_\<3>))
                (rr, (|std_bitset|_\<4>))
            )
        )
    )
    {
        BOOST_TEST_EQ(
            passed_by_lvalue_reference_to_const
          , U::evaluate_category<0>(args[_lrc])
        );
        BOOST_TEST_EQ(
            passed_by_lvalue_reference
          , U::evaluate_category<1>(args[_lr])
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference_to_const
          , U::evaluate_category<2>(
                args[_rrc0 | rvalue_const_bitset<2>()]
            )
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference
          , U::evaluate_category<3>(
                args[_rr0 | rvalue_bitset<3>()]
            )
        );

        return true;
    }
};

The following function calls are legal.

.. parsed-literal::

B::evaluate(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
  , rvalue_bitset<3>()
);
B::evaluate(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
);
B::evaluate((  // composed arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
));
B::evaluate(  // named arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
);
B::evaluate(  // named arguments
    _lr0 = lvalue_bitset<1>()
  , _lrc0 = lvalue_const_bitset<0>()
);

Because the parameters were wrapped in a (deduced …) clause, the following function calls are also legal.

.. parsed-literal::

B::evaluate(  // deduced arguments
    rvalue_bitset<3>()
  , lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
);
B::evaluate(  // deduced arguments
    lvalue_bitset<1>()
  , lvalue_const_bitset<0>()
);

The |preprocessor_cpp|_ test program demonstrates proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function.
name is the base name of the function; it determines the name of the generated forwarding functions. name may be qualified by the static keyword to declare the member function and its helpers as not associated with any object of the enclosing type.
tag_namespace is the namespace in which the keywords used by the function resides.
arguments is a |Boost_Preprocessor|_ sequence_ of argument-specifiers, as defined below.

Argument specifiers syntax:

.. parsed-literal::

argument-specifiers ::= *specifier-group0* {*specifier-group0*\ }

specifier-group0 ::= *specifier-group1* |
    (
        '**(**' '**deduced**'
            *specifier-group1* {*specifier-group1*\ }
        '**)**'
    )

specifier-group1 ::=
    (
        '**(**' '**optional**'
            *specifier* {*specifier*\ }
        '**)**'
    ) | (
        '**(**' '**required**'
            *specifier* {*specifier*\ }
        '**)**'
    )

specifier ::=
    '**(**' *argument-name* '**,**' *restriction* ')'

restriction ::=
    ( '**\***' '**(**' *mfc* '**)**' ) |
    ( '**(**' *type-name* '**)**' ) |
    '**\***'

argument-name is any valid C++ identifier.
mfc is an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|, and whose return type is a Boolean Integral Constant; however, user code cannot compute mfc in terms of previous-name ## _type.
type-name is either the name of a target type or an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|_, and whose return type is the target type.

Note that specifier does not include default-value. It is up to the function body to determine the default value of all optional arguments.

Approximate expansion:

Where:

n denotes the minimum arity, as determined from arguments.
m denotes the maximum arity, as determined from arguments.

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename Args>
using boost_param_result\_ ## __LINE__ ## **name** = **result**;

// If **result** is a simple return type:
template <typename Args>
struct boost_param_result\_ ## __LINE__ ## **name**
{
    typedef **result** type;
};

struct boost_param_params\_ ## __LINE__ ## **name**
  : |parameters|_\<
        *list of parameter specifications, based on arguments*
    >
{
};

typedef boost_param_params\_ ## __LINE__ ## **name**
    boost_param_parameters\_ ## __LINE__ ## **name**;

template <typename A0, …, typename A ## **n**>
**result** **name**\ (
    A0&& a0, …, A ## **n**\ && a ## **n**
  , typename boost_param_parameters\_ ## __LINE__ ## **name**
    ::match<A0, …, A ## **n**>::type
    = boost_param_parameters\_ ## __LINE__ ## **name**\ ()
)
{
    return this->boost_param_impl ## **name**\ (
        boost_param_parameters\_ ## __LINE__ ## **name**\ ()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **n**>(a ## **n**)
        )
    );
}

:vellipsis:`⋮`

template <typename A0, …, typename A ## **m**>
**result** **name**\ (
    A0&& a0, …, A ## **m**\ && a ## **m**
  , typename boost_param_parameters\_ ## __LINE__ ## **name**
    ::match<A0, …, A ## **m**>::type
    = boost_param_parameters\_ ## __LINE__ ## **name**\ ()
)
{
    return this->boost_param_impl ## **name**\ (
        boost_param_parameters\_ ## __LINE__ ## **name**\ ()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **m**>(a ## **m**)
        )
    );
}

template <typename Args>
typename boost_param_result\_ ## __LINE__ ## **name**\ <Args>::type
    boost_param_impl ## **name**\ (Args const& args)

Only the |ArgumentPack|_ type Args and its object instance args are available for use within the function body.

.. |BOOST_PARAMETER_BASIC_CONST_MEMBER_FUNCTION| replace:: BOOST_PARAMETER_BASIC_CONST_MEMBER_FUNCTION .. _BOOST_PARAMETER_BASIC_CONST_MEMBER_FUNCTION:

`BOOST_PARAMETER_BASIC_CONST_MEMBER_FUNCTION(result, name, tag_ns, args)`

:Defined in: |preprocessor_header|_

Generates a member function that can take in positional arguments, composed arguments, named arguments, and deduced arguments.

:Example usage:

The return type of each of the following function templates falls under a different value category.

.. parsed-literal::

template <std::size_t N>
|std_bitset|_\<N + 1> rvalue_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1> const rvalue_const_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1>& lvalue_bitset()
{
    static |std_bitset|_\<N + 1> lset = |std_bitset|_\<N + 1>();
    return lset;
}

template <std::size_t N>
|std_bitset|_\<N + 1> const& lvalue_const_bitset()
{
    static |std_bitset|_\<N + 1> const clset = |std_bitset|_\<N + 1>();
    return clset;
}

.. parsed-literal::

enum invoked
{
    passed_by_lvalue_reference_to_const
  , passed_by_lvalue_reference
  , passed_by_rvalue_reference_to_const
  , passed_by_rvalue_reference
};

struct U
{
    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&)
    {
        return passed_by_lvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&)
    {
        return passed_by_lvalue_reference;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&&)
    {
        return passed_by_rvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&&)
    {
        return passed_by_rvalue_reference;
    }
};

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\((_lrc, kw) in(lrc))
|BOOST_PARAMETER_NAME|_\((_lr, kw) in_out(lr))
|BOOST_PARAMETER_NAME|_\((_rrc, kw) in(rrc))
|BOOST_PARAMETER_NAME|_\((_rr, kw) consume(rr))

Use the macro as a substitute for a normal const member function header. Enclose the return type bool in parentheses. For each parameter, also enclose the expected value type in parentheses. Since the value types are mutually exclusive, you can wrap the parameters in a (deduced …) clause. Otherwise, just as with a normal function, the order in which you specify the parameters determines their position. However, unlike a normal function, default values must be specified within the function body. Also within the function body, you must pass the matching identifier with the leading underscore to the bracket operator of args to extract the corresponding argument, but at least this doesn't require std::forward to preserve value categories.

.. parsed-literal::

struct B
{
    B()
    {
    }

    BOOST_PARAMETER_BASIC_CONST_MEMBER_FUNCTION((bool), evaluate, kw,
        (deduced
            (required
                (lrc, (|std_bitset|_\<1>))
                (lr, (|std_bitset|_\<2>))
            )
            (optional
                (rrc, (|std_bitset|_\<3>))
                (rr, (|std_bitset|_\<4>))
            )
        )
    )
    {
        BOOST_TEST_EQ(
            passed_by_lvalue_reference_to_const
          , U::evaluate_category<0>(args[_lrc])
        );
        BOOST_TEST_EQ(
            passed_by_lvalue_reference
          , U::evaluate_category<1>(args[_lr])
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference_to_const
          , U::evaluate_category<2>(
                args[_rrc0 | rvalue_const_bitset<2>()]
            )
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference
          , U::evaluate_category<3>(
                args[_rr0 | rvalue_bitset<3>()]
            )
        );

        return true;
    }
};

The following function calls are legal.

.. parsed-literal::

B const b = B();
b.evaluate(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
  , rvalue_bitset<3>()
);
b.evaluate(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
);
b.evaluate((  // composed arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
));
b.evaluate(  // named arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
);
b.evaluate(  // named arguments
    _lr0 = lvalue_bitset<1>()
  , _lrc0 = lvalue_const_bitset<0>()
);

Because the parameters were wrapped in a (deduced …) clause, the following function calls are also legal.

.. parsed-literal::

b.evaluate(  // deduced arguments
    rvalue_bitset<3>()
  , lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
);
b.evaluate(  // deduced arguments
    lvalue_bitset<1>()
  , lvalue_const_bitset<0>()
);

The |preprocessor_cpp|_ test program demonstrates proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function.
name is the base name of the function; it determines the name of the generated forwarding functions.
tag_namespace is the namespace in which the keywords used by the function resides.
arguments is a |Boost_Preprocessor|_ sequence_ of argument-specifiers, as defined below.

Argument specifiers syntax:

.. parsed-literal::

argument-specifiers ::= *specifier-group0* {*specifier-group0*\ }

specifier-group0 ::= *specifier-group1* |
    (
        '**(**' '**deduced**'
            *specifier-group1* {*specifier-group1*\ }
        '**)**'
    )

specifier-group1 ::=
    (
        '**(**' '**optional**'
            *specifier* {*specifier*\ }
        '**)**'
    ) | (
        '**(**' '**required**'
            *specifier* {*specifier*\ }
        '**)**'
    )

specifier ::=
    '**(**' *argument-name* '**,**' *restriction* ')'

restriction ::=
    ( '**\***' '**(**' *mfc* '**)**' ) |
    ( '**(**' *type-name* '**)**' ) |
    '**\***'

argument-name is any valid C++ identifier.
mfc is an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|, and whose return type is a Boolean Integral Constant; however, user code cannot compute mfc in terms of previous-name ## _type.
type-name is either the name of a target type or an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|_, and whose return type is the target type.

Note that specifier does not include default-value. It is up to the function body to determine the default value of all optional arguments.

Approximate expansion:

Where:

n denotes the minimum arity, as determined from arguments.
m denotes the maximum arity, as determined from arguments.

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename Args>
using boost_param_result_const\_ ## __LINE__ ## **name** = **result**;

// If **result** is a simple return type:
template <typename Args>
struct boost_param_result_const\_ ## __LINE__ ## **name**
{
    typedef **result** type;
};

struct boost_param_params_const\_ ## __LINE__ ## **name**
  : |parameters|_\<
        *list of parameter specifications, based on arguments*
    >
{
};

typedef boost_param_params_const\_ ## __LINE__ ## **name**
    boost_param_parameters_const\_ ## __LINE__ ## **name**;

template <typename A0, …, typename A ## **n**>
**result** **name**\ (
    A0&& a0, …, A ## **n**\ && a ## **n**
  , typename boost_param_parameters_const\_ ## __LINE__ ## **name**
    ::match<A0, …, A ## **n**>::type
    = boost_param_parameters_const\_ ## __LINE__ ## **name**\ ()
) const
{
    return this->boost_param_impl_const ## __LINE__ ## **name**\ (
        boost_param_parameters_const\_ ## __LINE__ ## **name**\ ()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **n**>(a ## **n**)
        )
    );
}

:vellipsis:`⋮`

template <typename A0, …, typename A ## **m**>
**result** **name**\ (
    A0&& a0, …, A ## **m**\ && a ## **m**
  , typename boost_param_parameters_const\_ ## __LINE__ ## **name**
    ::match<A0, …, A ## **m**>::type
    = boost_param_parameters_const\_ ## __LINE__ ## **name**\ ()
) const
{
    return this->boost_param_impl_const ## __LINE__ ## **name**\ (
        boost_param_parameters_const\_ ## __LINE__ ## **name**\ ()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **m**>(a ## **m**)
        )
    );
}

template <typename Args>
typename boost_param_result_const\_ ## __LINE__ ## **name**\ <Args>::type
    boost_param_impl_const ## __LINE__ ## **name**\ (Args const& args) const

Only the |ArgumentPack|_ type Args and its object instance args are available for use within the function body.

.. |BOOST_PARAMETER_BASIC_FUNCTION_CALL_OPERATOR| replace:: BOOST_PARAMETER_BASIC_FUNCTION_CALL_OPERATOR .. _BOOST_PARAMETER_BASIC_FUNCTION_CALL_OPERATOR:

`BOOST_PARAMETER_BASIC_FUNCTION_CALL_OPERATOR(result, tag_ns, arguments)`

:Defined in: |preprocessor_header|_

Generates a function call operator that can take in positional arguments, composed arguments, named arguments, and deduced arguments.

:Example usage:

Define the named parameters that will comprise the argument specification that this macro will use. Ensure that all their tag types are in the same namespace, which is tag by default.

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\(y)
|BOOST_PARAMETER_NAME|_\(z)

.. parsed-literal::

class char_reader
{
    int index;
    char const* key;

 public:
    explicit char_reader(char const* k) : index(0), key(k)
    {
    }

    BOOST_PARAMETER_BASIC_FUNCTION_CALL_OPERATOR((void), tag,
        (deduced
            (required
                (y, (int))
                (z, (char const*))
            )
        )
    )
    {
        this->index = args[_y];
        this->key = args[_z];
    }

    |BOOST_PARAMETER_BASIC_CONST_FUNCTION_CALL_OPERATOR|_\((char), tag,
        (deduced
            (required
                (y, (bool))
                (z, (|std_map|_\<char const*, |std_string|_\>))
            )
        )
    )
    {
        return args[_y] ? (
            (args[_z].find(this->key)->second)[this->index]
        ) : this->key[this->index];
    }
};

As with regular argument-dependent lookup, the value types of the arguments passed in determine which function call operator overload gets invoked.

.. parsed-literal::

char const* keys[] = {"foo", "bar", "baz"};
|std_map|_\<char const*, |std_string|_\> k2s;
k2s[keys[0]] = |std_string|_\("qux");
k2s[keys[1]] = |std_string|_\("wmb");
k2s[keys[2]] = |std_string|_\("zxc");
char_reader r(keys[0]);

// positional arguments
BOOST_TEST_EQ('q', (r(true, k2s)));
BOOST_TEST_EQ('f', (r(false, k2s)));

// named arguments
r(_z = keys[1], _y = 1);
BOOST_TEST_EQ('m', (r(_z = k2s, _y = true)));
BOOST_TEST_EQ('a', (r(_z = k2s, _y = false)));

// deduced arguments
r(keys[2], 2);
BOOST_TEST_EQ('c', (r(k2s, true)));
BOOST_TEST_EQ('z', (r(k2s, false)));

The |preprocessor_cpp|_ test program demonstrates proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function call operator.
tag_namespace is the namespace in which the keywords used by the function call operator resides.
arguments is a |Boost_Preprocessor|_ sequence_ of argument-specifiers, as defined below.

Argument specifiers syntax:

.. parsed-literal::

argument-specifiers ::= *specifier-group0* {*specifier-group0*\ }

specifier-group0 ::= *specifier-group1* |
    (
        '**(**' '**deduced**'
            *specifier-group1* {*specifier-group1*\ }
        '**)**'
    )

specifier-group1 ::=
    (
        '**(**' '**optional**'
            *specifier* {*specifier*\ }
        '**)**'
    ) | (
        '**(**' '**required**'
            *specifier* {*specifier*\ }
        '**)**'
    )

specifier ::=
    '**(**' *argument-name* '**,**' *restriction* ')'

restriction ::=
    ( '**\***' '**(**' *mfc* '**)**' ) |
    ( '**(**' *type-name* '**)**' ) |
    '**\***'

argument-name is any valid C++ identifier.
mfc is an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|, and whose return type is a Boolean Integral Constant; however, user code cannot compute mfc in terms of previous-name ## _type.
type-name is either the name of a target type or an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|_, and whose return type is the target type.

Note that specifier does not include default-value. It is up to the function body to determine the default value of all optional arguments.

Approximate expansion:

Where:

n denotes the minimum arity, as determined from arguments.
m denotes the maximum arity, as determined from arguments.

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename Args>
using boost_param_result\_ ## __LINE__ ## operator = **result**;

// If **result** is a simple return type:
template <typename Args>
struct boost_param_result\_ ## __LINE__ ## operator
{
    typedef **result** type;
};

struct boost_param_params\_ ## __LINE__ ## operator
  : |parameters|_\<
        *list of parameter specifications, based on arguments*
    >
{
};

typedef boost_param_params\_ ## __LINE__ ## operator
    boost_param_parameters\_ ## __LINE__ ## operator;

template <typename A0, …, typename A ## **n**>
**result** operator()(
    A0&& a0, …, A ## **n**\ && a ## **n**
  , typename boost_param_parameters\_ ## __LINE__ ## operator::match<
        A0, …, A ## **n**
    >::type = boost_param_parameters\_ ## __LINE__ ## operator()
)
{
    return this->boost_param_impl ## __LINE__ ## operator(
        boost_param_parameters\_ ## __LINE__ ## operator()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **n**>(a ## **n**)
        )
    );
}

:vellipsis:`⋮`

template <typename A0, …, typename A ## **m**>
**result** operator()(
    A0&& a0, …, A ## **m**\ && a ## **m**
  , typename boost_param_parameters\_ ## __LINE__ ## operator::match<
        A0, …, A ## **m**
    >::type = boost_param_parameters\_ ## __LINE__ ## operator()
)
{
    return this->boost_param_impl ## __LINE__ ## operator(
        boost_param_parameters\_ ## __LINE__ ## operator()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **m**>(a ## **m**)
        )
    );
}

template <typename Args>
typename boost_param_result\_ ## __LINE__ ## operator<Args>::type
    boost_param_impl ## __LINE__ ## operator(Args const& args)

Only the |ArgumentPack|_ type Args and its object instance args are available for use within the function call operator body.

.. |BOOST_PARAMETER_BASIC_CONST_FUNCTION_CALL_OPERATOR| replace:: BOOST_PARAMETER_BASIC_CONST_FUNCTION_CALL_OPERATOR .. _BOOST_PARAMETER_BASIC_CONST_FUNCTION_CALL_OPERATOR:

`BOOST_PARAMETER_BASIC_CONST_FUNCTION_CALL_OPERATOR(result, tag_ns, args)`

:Defined in: |preprocessor_header|_

Generates a function call operator that can take in positional arguments, composed arguments, named arguments, and deduced arguments.

:Example usage:

The return type of each of the following function templates falls under a different value category.

.. parsed-literal::

template <std::size_t N>
|std_bitset|_\<N + 1> rvalue_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1> const rvalue_const_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1>& lvalue_bitset()
{
    static |std_bitset|_\<N + 1> lset = |std_bitset|_\<N + 1>();
    return lset;
}

template <std::size_t N>
|std_bitset|_\<N + 1> const& lvalue_const_bitset()
{
    static |std_bitset|_\<N + 1> const clset = |std_bitset|_\<N + 1>();
    return clset;
}

.. parsed-literal::

enum invoked
{
    passed_by_lvalue_reference_to_const
  , passed_by_lvalue_reference
  , passed_by_rvalue_reference_to_const
  , passed_by_rvalue_reference
};

struct U
{
    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&)
    {
        return passed_by_lvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&)
    {
        return passed_by_lvalue_reference;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&&)
    {
        return passed_by_rvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&&)
    {
        return passed_by_rvalue_reference;
    }
};

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\((_lrc, kw) in(lrc))
|BOOST_PARAMETER_NAME|_\((_lr, kw) in_out(lr))
|BOOST_PARAMETER_NAME|_\((_rrc, kw) in(rrc))
|BOOST_PARAMETER_NAME|_\((_rr, kw) consume(rr))

Use the macro as a substitute for a normal const function call operator header. Enclose the return type bool in parentheses. For each parameter, also enclose the expected value type in parentheses. Since the value types are mutually exclusive, you can wrap the parameters in a (deduced …) clause. Otherwise, just as with a normal function, the order in which you specify the parameters determines their position. However, unlike a normal function, default values must be specified within the function body. Also within the function body, you must pass the matching identifier with the leading underscore to the bracket operator of args to extract the corresponding argument, but at least this doesn't require std::forward to preserve value categories.

.. parsed-literal::

struct B
{
    B()
    {
    }

    BOOST_PARAMETER_BASIC_CONST_FUNCTION_CALL_OPERATOR((bool), kw,
        (deduced
            (required
                (lrc, (|std_bitset|_\<1>))
                (lr, (|std_bitset|_\<2>))
            )
            (optional
                (rrc, (|std_bitset|_\<3>))
                (rr, (|std_bitset|_\<4>))
            )
        )
    )
    {
        BOOST_TEST_EQ(
            passed_by_lvalue_reference_to_const
          , U::evaluate_category<0>(args[_lrc])
        );
        BOOST_TEST_EQ(
            passed_by_lvalue_reference
          , U::evaluate_category<1>(args[_lr])
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference_to_const
          , U::evaluate_category<2>(
                args[_rrc0 | rvalue_const_bitset<2>()]
            )
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference
          , U::evaluate_category<3>(
                args[_rr0 | rvalue_bitset<3>()]
            )
        );

        return true;
    }
};

The following function calls are legal.

.. parsed-literal::

B const b = B();
b(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
  , rvalue_bitset<3>()
);
b(  // positional arguments
    lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
);
b((  // composed arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
));
b(  // named arguments
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
);
b(  // named arguments
    _lr0 = lvalue_bitset<1>()
  , _lrc0 = lvalue_const_bitset<0>()
);

Because the parameters were wrapped in a (deduced …) clause, the following function calls are also legal.

.. parsed-literal::

b(  // deduced arguments
    rvalue_bitset<3>()
  , lvalue_const_bitset<0>()
  , lvalue_bitset<1>()
  , rvalue_const_bitset<2>()
);
b(  // deduced arguments
    lvalue_bitset<1>()
  , lvalue_const_bitset<0>()
);

The |preprocessor_cpp|_ test program demonstrates proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function call operator.
tag_namespace is the namespace in which the keywords used by the function call operator resides.
arguments is a |Boost_Preprocessor|_ sequence_ of argument-specifiers, as defined below.

Argument specifiers syntax:

.. parsed-literal::

argument-specifiers ::= *specifier-group0* {*specifier-group0*\ }

specifier-group0 ::= *specifier-group1* |
    (
        '**(**' '**deduced**'
            *specifier-group1* {*specifier-group1*\ }
        '**)**'
    )

specifier-group1 ::=
    (
        '**(**' '**optional**'
            *specifier* {*specifier*\ }
        '**)**'
    ) | (
        '**(**' '**required**'
            *specifier* {*specifier*\ }
        '**)**'
    )

specifier ::=
    '**(**' *argument-name* '**,**' *restriction* ')'

restriction ::=
    ( '**\***' '**(**' *mfc* '**)**' ) |
    ( '**(**' *type-name* '**)**' ) |
    '**\***'

argument-name is any valid C++ identifier.
mfc is an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|, and whose return type is a Boolean Integral Constant; however, user code cannot compute mfc in terms of previous-name ## _type.
type-name is either the name of a target type or an MPL Binary Metafunction Class_ whose first argument will be the type of the corresponding argument-name, whose second argument will be the entire |ArgumentPack|_, and whose return type is the target type.

Note that specifier does not include default-value. It is up to the function body to determine the default value of all optional arguments.

Approximate expansion:

Where:

n denotes the minimum arity, as determined from arguments.
m denotes the maximum arity, as determined from arguments.

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename Args>
using boost_param_result_const\_ ## __LINE__ ## operator = **result**;

// If **result** is a simple return type:
template <typename Args>
struct boost_param_result_const\_ ## __LINE__ ## operator
{
    typedef **result** type;
};

struct boost_param_params_const\_ ## __LINE__ ## operator
  : |parameters|_\<
        *list of parameter specifications, based on arguments*
    >
{
};

typedef boost_param_params_const\_ ## __LINE__ ## operator
    boost_param_parameters_const\_ ## __LINE__ ## operator;

template <typename A0, …, typename A ## **n**>
**result** operator()(
    A0&& a0, …, A ## **n**\ && a ## **n**
  , typename boost_param_parameters_const\_ ## __LINE__ ## operator
    ::match<A0, …, A ## **n**>::type
    = boost_param_parameters_const\_ ## __LINE__ ## operator()
) const
{
    return this->boost_param_impl_const ## __LINE__ ## operator(
        boost_param_parameters_const\_ ## __LINE__ ## operator()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **n**>(a ## **n**)
        )
    );
}

:vellipsis:`⋮`

template <typename A0, …, typename A ## **m**>
**result** operator()(
    A0&& a0, …, A ## **m**\ && a ## **m**
  , typename boost_param_parameters_const\_ ## __LINE__ ## operator
    ::match<A0, …, A ## **m**>::type
    = boost_param_parameters_const\_ ## __LINE__ ## operator()
) const
{
    return this->boost_param_impl_const ## __LINE__ ## operator(
        boost_param_parameters_const\_ ## __LINE__ ## operator()(
            |std_forward|_\<A0>(a0)
          , …
          , |std_forward|_\<A ## **m**>(a ## **m**)
        )
    );
}

template <typename Args>
typename boost_param_result_const\_ ## __LINE__ ## operator<Args>::type
    boost_param_impl_const ## __LINE__ ## operator(Args const& args) const

Only the |ArgumentPack|_ type Args and its object instance args are available for use within the function call operator body.

.. |BOOST_PARAMETER_NO_SPEC_FUNCTION| replace:: BOOST_PARAMETER_NO_SPEC_FUNCTION .. _BOOST_PARAMETER_NO_SPEC_FUNCTION:

`BOOST_PARAMETER_NO_SPEC_FUNCTION(result, name)`

:Defined in: |preprocessor_no_spec_header|_

Generates a function that can take in named arguments.

:Example usage:

The return type of each of the following function templates falls under a different value category.

.. parsed-literal::

template <std::size_t N>
|std_bitset|_\<N + 1> rvalue_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1> const rvalue_const_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1>& lvalue_bitset()
{
    static |std_bitset|_\<N + 1> lset = |std_bitset|_\<N + 1>();
    return lset;
}

template <std::size_t N>
|std_bitset|_\<N + 1> const& lvalue_const_bitset()
{
    static |std_bitset|_\<N + 1> const clset = |std_bitset|_\<N + 1>();
    return clset;
}

.. parsed-literal::

enum invoked
{
    passed_by_lvalue_reference_to_const
  , passed_by_lvalue_reference
  , passed_by_rvalue_reference_to_const
  , passed_by_rvalue_reference
};

struct U
{
    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&)
    {
        return passed_by_lvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&)
    {
        return passed_by_lvalue_reference;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&&)
    {
        return passed_by_rvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&&)
    {
        return passed_by_rvalue_reference;
    }
};

Named parameters are required when invoking the function; however, none of their tags need to be in the same namespace.

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\((_lrc, kw0) in(lrc))
|BOOST_PARAMETER_NAME|_\((_lr, kw1) in_out(lr))
|BOOST_PARAMETER_NAME|_\((_rrc, kw2) in(rrc))
|BOOST_PARAMETER_NAME|_\((_rr, kw3) consume(rr))

Use the macro as a substitute for a variadic function header. Enclose the return type bool in parentheses.

.. parsed-literal::

BOOST_PARAMETER_NO_SPEC_FUNCTION((bool), evaluate)
{
    BOOST_TEST_EQ(
        passed_by_lvalue_reference_to_const
      , U::evaluate_category<0>(args[_lrc])
    );
    BOOST_TEST_EQ(
        passed_by_lvalue_reference
      , U::evaluate_category<1>(args[_lr])
    );
    BOOST_TEST_EQ(
        passed_by_rvalue_reference_to_const
      , U::evaluate_category<2>(
            args[_rrc | rvalue_const_bitset<2>()]
        )
    );
    BOOST_TEST_EQ(
        passed_by_rvalue_reference
      , U::evaluate_category<3>(args[_rr | rvalue_bitset<3>()])
    );

    return true;
}

To invoke the function, bind all its arguments to named parameters.

.. parsed-literal::

evaluate(
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
);
evaluate(
    _lr0 = lvalue_bitset<1>()
  , _lrc0 = lvalue_const_bitset<0>()
);

The |preproc_eval_cat_no_spec_cpp|_ test program demonstrates proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function.
name is the base name of the function; it determines the name of the generated implementation function.

Argument specifiers syntax:

None.

Approximate expansion:

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename TaggedArg0, typename ...TaggedArgs>
using boost_param_no_spec_result\_ ## __LINE__ ## **name** = **result**;

// If **result** is a simple return type:
template <typename TaggedArg0, typename ...TaggedArgs>
struct boost_param_no_spec_result\_ ## __LINE__ ## **name**
{
    typedef **result** type;
};

template <typename ResultType, typename Args>
ResultType
    boost_param_no_spec_impl ## __LINE__ ## **name**\ (
        (ResultType(*)())
      , Args const& args
    );

template <typename TaggedArg0, typename ...TaggedArgs>
inline typename |boost_lazy_enable_if|_\<
    |are_tagged_arguments|_\<TaggedArg0,TaggedArgs...>
  , boost_param_no_spec_result\_ ## __LINE__ ## **name**\ <
        TaggedArg0
      , TaggedArgs...
    >
>::type
    **name**\ (TaggedArg0 const& arg0, TaggedArgs const&... args)
{
    return boost_param_no_spec_impl ## __LINE__ ## **name**\ (
        static_cast<
            typename
            boost_param_no_spec_result\_ ## __LINE__ ## **name**\ <
                TaggedArg0
              , TaggedArgs...
            >::type(*)()
        >(|std_nullptr|_\)
      , |compose|_\(arg0, args...)
    );
}

template <typename ResultType, typename Args>
ResultType
    boost_param_no_spec_impl ## __LINE__ ## **name**\ (
        (ResultType(*)())
      , Args const& args
    )

Only the |ArgumentPack|_ type Args and its object instance args are available for use within the function body.

.. |BOOST_PARAMETER_NO_SPEC_MEMBER_FUNCTION| replace:: BOOST_PARAMETER_NO_SPEC_MEMBER_FUNCTION .. _BOOST_PARAMETER_NO_SPEC_MEMBER_FUNCTION:

`BOOST_PARAMETER_NO_SPEC_MEMBER_FUNCTION(result, name)`

:Defined in: |preprocessor_no_spec_header|_

Generates a member function that can take in named arguments.

:Example usage:

When designing a front-end class template whose back-end is configurable via parameterized inheritance, it can be useful to omit argument specifiers from a named-parameter member function so that the delegate member functions of the back-end classes can enforce their own specifications.

.. parsed-literal::

template <typename B>
struct frontend : B
{
    frontend() : B()
    {
    }

    BOOST_PARAMETER_NO_SPEC_MEMBER_FUNCTION((void), initialize)
    {
        this->initialize_impl(args);
    }
};

Named parameters are required when invoking the member function; however, none of their tags need to be in the same namespace.

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\(a0)
|BOOST_PARAMETER_NAME|_\(a1)
|BOOST_PARAMETER_NAME|_\(a2)

For this example, each of the back-end class templates requires its own parameter to be present in the argument pack. In practice, such parameters should be optional, with default values.

.. parsed-literal::

template <typename T>
class backend0
{
    T a0;

 public:
    backend0() : a0()
    {
    }

    T const& get_a0() const
    {
        return this->a0;
    }

 protected:
    template <typename ArgPack>
    void initialize_impl(ArgPack const& args)
    {
        this->a0 = args[_a0];
    }
};

template <typename B, typename T>
class backend1 : public B
{
    T a1;

 public:
    backend1() : B(), a1()
    {
    }

    T const& get_a1() const
    {
        return this->a1;
    }

 protected:
    template <typename ArgPack>
    void initialize_impl(ArgPack const& args)
    {
        B::initialize_impl(args);
        this->a1 = args[_a1];
    }
};

template <typename B, typename T>
class backend2 : public B
{
    T a2;

 public:
    backend2() : B(), a2()
    {
    }

    T const& get_a2() const
    {
        return this->a2;
    }

 protected:
    template <typename ArgPack>
    void initialize_impl(ArgPack const& args)
    {
        B::initialize_impl(args);
        this->a2 = args[_a2];
    }
};

This example shows that while backend0 must always be the root base class template and that frontend must always be the most derived class template, the other back-ends can be chained together in different orders.

.. parsed-literal::

char const* p = "foo";
frontend<
    backend2<backend1<backend0<char const*>, char>, int>
> composed_obj0;
frontend<
    backend1<backend2<backend0<char const*>, int>, char>
> composed_obj1;
composed_obj0.initialize(_a2 = 4, _a1 = ' ', _a0 = p);
composed_obj1.initialize(_a0 = p, _a1 = ' ', _a2 = 4);
BOOST_TEST_EQ(composed_obj0.get_a0(), composed_obj1.get_a0());
BOOST_TEST_EQ(composed_obj0.get_a1(), composed_obj1.get_a1());
BOOST_TEST_EQ(composed_obj0.get_a2(), composed_obj1.get_a2());

The |parameterized_inheritance_cpp|_ and |preproc_eval_cat_no_spec_cpp|_ test programs demonstrate proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function.
name is the base name of the function; it determines the name of the generated implementation function. name may be qualified by the static keyword to declare the member function and its helpers as not associated with any object of the enclosing type.

Argument specifiers syntax:

None.

Approximate expansion:

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename TaggedArg0, typename ...TaggedArgs>
using boost_param_no_spec_result\_ ## __LINE__ ## **name** = **result**;

// If **result** is a simple return type:
template <typename TaggedArg0, typename ...TaggedArgs>
struct boost_param_no_spec_result\_ ## __LINE__ ## **name**
{
    typedef **result** type;
};

template <typename TaggedArg0, typename ...TaggedArgs>
inline typename |boost_lazy_enable_if|_\<
    |are_tagged_arguments|_\<TaggedArg0,TaggedArgs...>
  , boost_param_no_spec_result\_ ## __LINE__ ## **name**\ <
        TaggedArg0
      , TaggedArgs...
    >
>::type
    **name**\ (TaggedArg0 const& arg0, TaggedArgs const&... args)
{
    return this->boost_param_no_spec_impl ## __LINE__ ## **name**\ (
        static_cast<
            typename
            boost_param_no_spec_result\_ ## __LINE__ ## **name**\ <
                TaggedArg0
              , TaggedArgs...
            >::type(*)()
        >(|std_nullptr|_\)
      , |compose|_\(arg0, args...)
    );
}

template <typename ResultType, typename Args>
ResultType
    boost_param_no_spec_impl ## __LINE__ ## **name**\ (
        (ResultType(*)())
      , Args const& args
    )

Only the |ArgumentPack|_ type Args and its object instance args are available for use within the function body.

.. |BOOST_PARAMETER_NO_SPEC_CONST_MEMBER_FUNCTION| replace:: BOOST_PARAMETER_NO_SPEC_CONST_MEMBER_FUNCTION .. _BOOST_PARAMETER_NO_SPEC_CONST_MEMBER_FUNCTION:

`BOOST_PARAMETER_NO_SPEC_CONST_MEMBER_FUNCTION(result, name)`

:Defined in: |preprocessor_no_spec_header|_

Generates a member function that can take in named arguments.

:Example usage:

The return type of each of the following function templates falls under a different value category.

.. parsed-literal::

template <std::size_t N>
|std_bitset|_\<N + 1> rvalue_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1> const rvalue_const_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1>& lvalue_bitset()
{
    static |std_bitset|_\<N + 1> lset = |std_bitset|_\<N + 1>();
    return lset;
}

template <std::size_t N>
|std_bitset|_\<N + 1> const& lvalue_const_bitset()
{
    static |std_bitset|_\<N + 1> const clset = |std_bitset|_\<N + 1>();
    return clset;
}

.. parsed-literal::

enum invoked
{
    passed_by_lvalue_reference_to_const
  , passed_by_lvalue_reference
  , passed_by_rvalue_reference_to_const
  , passed_by_rvalue_reference
};

struct U
{
    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&)
    {
        return passed_by_lvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&)
    {
        return passed_by_lvalue_reference;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&&)
    {
        return passed_by_rvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&&)
    {
        return passed_by_rvalue_reference;
    }
};

Named parameters are required when invoking the member function; however, none of their tags need to be in the same namespace.

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\((_lrc, kw0) in(lrc))
|BOOST_PARAMETER_NAME|_\((_lr, kw1) in_out(lr))
|BOOST_PARAMETER_NAME|_\((_rrc, kw2) in(rrc))
|BOOST_PARAMETER_NAME|_\((_rr, kw3) consume(rr))

Use the macro as a substitute for a variadic function header. Enclose the return type bool in parentheses. The macro will qualify the function with the const keyword.

.. parsed-literal::

struct D
{
    D()
    {
    }

    BOOST_PARAMETER_NO_SPEC_CONST_MEMBER_FUNCTION((bool), evaluate_m)
    {
        BOOST_TEST_EQ(
            passed_by_lvalue_reference_to_const
          , U::evaluate_category<0>(args[_lrc])
        );
        BOOST_TEST_EQ(
            passed_by_lvalue_reference
          , U::evaluate_category<1>(args[_lr])
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference_to_const
          , U::evaluate_category<2>(
                args[_rrc | rvalue_const_bitset<2>()]
            )
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference
          , U::evaluate_category<3>(
                args[_rr | rvalue_bitset<3>()]
            )
        );

        return true;
    }
};

To invoke the member function, bind all its arguments to named parameters.

.. parsed-literal::

D const d = D();
d.evaluate_m(
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
);
d.evaluate_m(
    _lr0 = lvalue_bitset<1>()
  , _lrc0 = lvalue_const_bitset<0>()
);

The |preproc_eval_cat_no_spec_cpp|_ test program demonstrates proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function.
name is the base name of the function; it determines the name of the generated implementation function.

Argument specifiers syntax:

None.

Approximate expansion:

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename TaggedArg0, typename ...TaggedArgs>
using boost_param_no_spec_result_const\_ ## __LINE__ ## **name** = **result**;

// If **result** is a simple return type:
template <typename TaggedArg0, typename ...TaggedArgs>
struct boost_param_no_spec_result_const\_ ## __LINE__ ## **name**
{
    typedef **result** type;
};

template <typename TaggedArg0, typename ...TaggedArgs>
inline typename |boost_lazy_enable_if|_\<
    |are_tagged_arguments|_\<TaggedArg0,TaggedArgs...>
  , boost_param_no_spec_result_const\_ ## __LINE__ ## **name**\ <
        TaggedArg0
      , TaggedArgs...
    >
>::type
    **name**\ (TaggedArg0 const& arg0, TaggedArgs const&... args) const
{
    return this->boost_param_no_spec_impl_const ## __LINE__ ## **name**\ (
        static_cast<
            typename
            boost_param_no_spec_result_const\_ ## __LINE__ ## **name**\ <
                TaggedArg0
              , TaggedArgs...
            >::type(*)()
        >(|std_nullptr|_\)
      , |compose|_\(arg0, args...)
    );
}

template <typename ResultType, typename Args>
ResultType
    boost_param_no_spec_impl_const ## __LINE__ ## **name**\ (
        (ResultType(*)())
      , Args const& args
    ) const

Only the |ArgumentPack|_ type Args and its object instance args are available for use within the function body.

.. |BOOST_PARAMETER_NO_SPEC_FUNCTION_CALL_OPERATOR| replace:: BOOST_PARAMETER_NO_SPEC_FUNCTION_CALL_OPERATOR .. _BOOST_PARAMETER_NO_SPEC_FUNCTION_CALL_OPERATOR:

`BOOST_PARAMETER_NO_SPEC_FUNCTION_CALL_OPERATOR(result)`

:Defined in: |preprocessor_no_spec_header|_

Generates a function call operator that can take in named arguments.

:Example usage:

When designing a front-end class template whose back-end is configurable via parameterized inheritance, it can be useful to omit argument specifiers from a named-parameter function call operator so that the delegate member functions of the back-end classes can enforce their own specifications.

.. parsed-literal::

template <typename B>
struct frontend : B
{
    frontend() : B()
    {
    }

    BOOST_PARAMETER_NO_SPEC_FUNCTION_CALL_OPERATOR((void))
    {
        this->initialize_impl(args);
    }
};

Named parameters are required when invoking the function call operator; however, none of their tags need to be in the same namespace.

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\(a0)
|BOOST_PARAMETER_NAME|_\(a1)
|BOOST_PARAMETER_NAME|_\(a2)

For this example, each of the back-end class templates requires its own parameter to be present in the argument pack. In practice, such parameters should be optional, with default values.

.. parsed-literal::

template <typename T>
class backend0
{
    T a0;

 public:
    backend0() : a0()
    {
    }

    T const& get_a0() const
    {
        return this->a0;
    }

 protected:
    template <typename ArgPack>
    void initialize_impl(ArgPack const& args)
    {
        this->a0 = args[_a0];
    }
};

template <typename B, typename T>
class backend1 : public B
{
    T a1;

 public:
    backend1() : B(), a1()
    {
    }

    T const& get_a1() const
    {
        return this->a1;
    }

 protected:
    template <typename ArgPack>
    void initialize_impl(ArgPack const& args)
    {
        B::initialize_impl(args);
        this->a1 = args[_a1];
    }
};

template <typename B, typename T>
class backend2 : public B
{
    T a2;

 public:
    backend2() : B(), a2()
    {
    }

    T const& get_a2() const
    {
        return this->a2;
    }

 protected:
    template <typename ArgPack>
    void initialize_impl(ArgPack const& args)
    {
        B::initialize_impl(args);
        this->a2 = args[_a2];
    }
};

.. parsed-literal::

char const* p = "foo";
frontend<
    backend2<backend1<backend0<char const*>, char>, int>
> composed_obj0;
frontend<
    backend1<backend2<backend0<char const*>, int>, char>
> composed_obj1;
composed_obj0(_a2 = 4, _a1 = ' ', _a0 = p);
composed_obj1(_a0 = p, _a1 = ' ', _a2 = 4);
BOOST_TEST_EQ(composed_obj0.get_a0(), composed_obj1.get_a0());
BOOST_TEST_EQ(composed_obj0.get_a1(), composed_obj1.get_a1());
BOOST_TEST_EQ(composed_obj0.get_a2(), composed_obj1.get_a2());

The |parameterized_inheritance_cpp|_ and |preproc_eval_cat_no_spec_cpp|_ test programs demonstrate proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function call operator.

Argument specifiers syntax:

None.

Approximate expansion:

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename TaggedArg0, typename ...TaggedArgs>
using boost_param_no_spec_result\_ ## __LINE__ ## operator = **result**;

// If **result** is a simple return type:
template <typename TaggedArg0, typename ...TaggedArgs>
struct boost_param_no_spec_result\_ ## __LINE__ ## operator
{
    typedef **result** type;
};

template <typename TaggedArg0, typename ...TaggedArgs>
inline typename |boost_lazy_enable_if|_\<
    |are_tagged_arguments|_\<TaggedArg0,TaggedArgs...>
  , boost_param_no_spec_result\_ ## __LINE__ ## operator<
        TaggedArg0
      , TaggedArgs...
    >
>::type
    operator()(TaggedArg0 const& arg0, TaggedArgs const&... args)
{
    return this->boost_param_no_spec_impl ## __LINE__ ## operator(
        static_cast<
            typename
            boost_param_no_spec_result\_ ## __LINE__ ## operator<
                TaggedArg0
              , TaggedArgs...
            >::type(*)()
        >(|std_nullptr|_\)
      , |compose|_\(arg0, args...)
    );
}

template <typename ResultType, typename Args>
ResultType
    boost_param_no_spec_impl ## __LINE__ ## operator(
        (ResultType(*)())
      , Args const& args
    )

Only the |ArgumentPack|_ type Args and its object instance args are available for use within the function body.

.. |BOOST_PARAMETER_NO_SPEC_CONST_FUNCTION_CALL_OPERATOR| replace:: BOOST_PARAMETER_NO_SPEC_CONST_FUNCTION_CALL_OPERATOR .. _BOOST_PARAMETER_NO_SPEC_CONST_FUNCTION_CALL_OPERATOR:

`BOOST_PARAMETER_NO_SPEC_CONST_FUNCTION_CALL_OPERATOR(result)`

:Defined in: |preprocessor_no_spec_header|_

Generates a function call operator that can take in named arguments.

:Example usage:

The return type of each of the following function templates falls under a different value category.

.. parsed-literal::

template <std::size_t N>
|std_bitset|_\<N + 1> rvalue_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1> const rvalue_const_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1>& lvalue_bitset()
{
    static |std_bitset|_\<N + 1> lset = |std_bitset|_\<N + 1>();
    return lset;
}

template <std::size_t N>
|std_bitset|_\<N + 1> const& lvalue_const_bitset()
{
    static |std_bitset|_\<N + 1> const clset = |std_bitset|_\<N + 1>();
    return clset;
}

.. parsed-literal::

enum invoked
{
    passed_by_lvalue_reference_to_const
  , passed_by_lvalue_reference
  , passed_by_rvalue_reference_to_const
  , passed_by_rvalue_reference
};

struct U
{
    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&)
    {
        return passed_by_lvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&)
    {
        return passed_by_lvalue_reference;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&&)
    {
        return passed_by_rvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&&)
    {
        return passed_by_rvalue_reference;
    }
};

Named parameters are required when invoking the function call operator; however, none of their tags need to be in the same namespace.

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\((_lrc, kw0) in(lrc))
|BOOST_PARAMETER_NAME|_\((_lr, kw1) in_out(lr))
|BOOST_PARAMETER_NAME|_\((_rrc, kw2) in(rrc))
|BOOST_PARAMETER_NAME|_\((_rr, kw3) consume(rr))

Use the macro as a substitute for a variadic function call operator header. Enclose the return type bool in parentheses. The macro will qualify the function with the const keyword.

.. parsed-literal::

struct D
{
    D()
    {
    }

    BOOST_PARAMETER_NO_SPEC_CONST_FUNCTION_CALL_OPERATOR((bool))
    {
        BOOST_TEST_EQ(
            passed_by_lvalue_reference_to_const
          , U::evaluate_category<0>(args[_lrc])
        );
        BOOST_TEST_EQ(
            passed_by_lvalue_reference
          , U::evaluate_category<1>(args[_lr])
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference_to_const
          , U::evaluate_category<2>(
                args[_rrc | rvalue_const_bitset<2>()]
            )
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference
          , U::evaluate_category<3>(
                args[_rr | rvalue_bitset<3>()]
            )
        );

        return true;
    }
};

To invoke the function call operator, bind all its arguments to named parameters.

.. parsed-literal::

D const d = D();
d(
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
);
d(
    _lr0 = lvalue_bitset<1>()
  , _lrc0 = lvalue_const_bitset<0>()
);

The |preproc_eval_cat_no_spec_cpp|_ test program demonstrates proper usage of this macro.

Macro parameters:

result is the parenthesized return type of the function call operator.

Argument specifiers syntax:

None.

Approximate expansion:

.. parsed-literal::

// If **result** is a template instantiation of |boost_enable_if|_\,
// |boost_enable_if_c|_\, |boost_lazy_enable_if|_\,
// |boost_lazy_enable_if_c|_\, |boost_disable_if|_\, |boost_disable_if_c|_\,
// |boost_lazy_disable_if|_\, |boost_lazy_disable_if_c|_\, or
// |std_enable_if|_\:
template <typename TaggedArg0, typename ...TaggedArgs>
using boost_param_no_spec_result_const\_ ## __LINE__ ## operator = **result**;

// If **result** is a simple return type:
template <typename TaggedArg0, typename ...TaggedArgs>
struct boost_param_no_spec_result_const\_ ## __LINE__ ## operator
{
    typedef **result** type;
};

template <typename TaggedArg0, typename ...TaggedArgs>
inline typename |boost_lazy_enable_if|_\<
    |are_tagged_arguments|_\<TaggedArg0,TaggedArgs...>
  , boost_param_no_spec_result_const\_ ## __LINE__ ## operator<
        TaggedArg0
      , TaggedArgs...
    >
>::type
    operator()(
        TaggedArg0 const& arg0
      , TaggedArgs const&... args
    ) const
{
    return this->boost_param_no_spec_impl_const ## __LINE__ ## operator(
        static_cast<
            typename
            boost_param_no_spec_result_const\_ ## __LINE__ ## operator<
                TaggedArg0
              , TaggedArgs...
            >::type(*)()
        >(|std_nullptr|_\)
      , |compose|_\(arg0, args...)
    );
}

template <typename ResultType, typename Args>
ResultType
    boost_param_no_spec_impl_const ## __LINE__ ## operator(
        (ResultType(*)())
      , Args const& args
    ) const

Only the |ArgumentPack|_ type Args and its object instance args are available for use within the function body.

.. |BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR| replace:: BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR .. _BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR:

`BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR(cls, impl)`

:Defined in: |preprocessor_no_spec_header|_

Generates a constructor that can take in named arguments.

:Example usage:

When designing a front-end class template whose back-end is configurable via parameterized inheritance, it can be useful to omit argument specifiers from a named-parameter constructor so that the delegate constructors of the back-end classes can enforce their own specifications.

.. parsed-literal::

template <typename B>
struct frontend : B
{
    BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR(frontend, (B))
};

Named parameters are required when invoking the constructor; however, none of their tags need to be in the same namespace.

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\(a0)
|BOOST_PARAMETER_NAME|_\(a1)
|BOOST_PARAMETER_NAME|_\(a2)

For this example, each of the back-end class templates requires its own parameter to be present in the argument pack. In practice, such parameters should be optional, with default values.

.. parsed-literal::

struct _enabler
{
};

template <typename T>
class backend0
{
    T a0;

 public:
    template <typename ArgPack>
    explicit backend0(
        ArgPack const& args
      , typename |boost_enable_if|_\<
            |is_argument_pack|_\<ArgPack>
          , _enabler
        >::type = _enabler()
    ) : a0(args[_a0])
    {
    }

    T const& get_a0() const
    {
        return this->a0;
    }
};

template <typename B, typename T>
class backend1 : public B
{
    T a1;

 public:
    template <typename ArgPack>
    explicit backend1(
        ArgPack const& args
      , typename |boost_enable_if|_\<
            |is_argument_pack|_\<ArgPack>
          , _enabler
        >::type = _enabler()
    ) : B(args), a1(args[_a1])
    {
    }

    T const& get_a1() const
    {
        return this->a1;
    }
};

template <typename B, typename T>
class backend2 : public B
{
    T a2;

 public:
    template <typename ArgPack>
    explicit backend2(
        ArgPack const& args
      , typename |boost_enable_if|_\<
            |is_argument_pack|_\<ArgPack>
          , _enabler
        >::type = _enabler()
    ) : B(args), a2(args[_a2])
    {
    }

    T const& get_a2() const
    {
        return this->a2;
    }
};

.. parsed-literal::

char const* p = "foo";
frontend<
    backend2<backend1<backend0<char const*>, char>, int>
> composed_obj0(_a2 = 4, _a1 = ' ', _a0 = p);
frontend<
    backend1<backend2<backend0<char const*>, int>, char>
> composed_obj1(_a0 = p, _a1 = ' ', _a2 = 4);
BOOST_TEST_EQ(composed_obj0.get_a0(), composed_obj1.get_a0());
BOOST_TEST_EQ(composed_obj0.get_a1(), composed_obj1.get_a1());
BOOST_TEST_EQ(composed_obj0.get_a2(), composed_obj1.get_a2());

The |parameterized_inheritance_cpp|_ and |preproc_eval_cat_no_spec_cpp|_ test programs demonstrate proper usage of this macro.

Macro parameters:

cls is the name of the enclosing class.
impl is the parenthesized implementation base class for cls.

Argument specifiers syntax:

None.

Approximate expansion:

.. parsed-literal::

template <
    typename TaggedArg0
  , typename ...TaggedArgs
  , typename = typename |boost_enable_if|_\<
        |are_tagged_arguments|_\<TaggedArg0,TaggedArgs...>
    >::type
>
inline explicit **cls**\ (
    TaggedArg0 const& arg0
  , TaggedArgs const&... args
) : **impl**\ (|compose|_\(arg0, args...))
{
}

.. |BOOST_PARAMETER_NO_SPEC_NO_BASE_CONSTRUCTOR| replace:: BOOST_PARAMETER_NO_SPEC_NO_BASE_CONSTRUCTOR .. _BOOST_PARAMETER_NO_SPEC_NO_BASE_CONSTRUCTOR:

`BOOST_PARAMETER_NO_SPEC_NO_BASE_CONSTRUCTOR(cls, impl)`

:Defined in: |preprocessor_no_spec_header|_

Generates a constructor that can take in named arguments.

:Example usage:

The return type of each of the following function templates falls under a different value category.

.. parsed-literal::

template <std::size_t N>
|std_bitset|_\<N + 1> rvalue_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1> const rvalue_const_bitset()
{
    return |std_bitset|_\<N + 1>();
}

template <std::size_t N>
|std_bitset|_\<N + 1>& lvalue_bitset()
{
    static |std_bitset|_\<N + 1> lset = |std_bitset|_\<N + 1>();
    return lset;
}

template <std::size_t N>
|std_bitset|_\<N + 1> const& lvalue_const_bitset()
{
    static |std_bitset|_\<N + 1> const clset = |std_bitset|_\<N + 1>();
    return clset;
}

.. parsed-literal::

enum invoked
{
    passed_by_lvalue_reference_to_const
  , passed_by_lvalue_reference
  , passed_by_rvalue_reference_to_const
  , passed_by_rvalue_reference
};

struct U
{
    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&)
    {
        return passed_by_lvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&)
    {
        return passed_by_lvalue_reference;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1> const&&)
    {
        return passed_by_rvalue_reference_to_const;
    }

    template <std::size_t N>
    static invoked evaluate_category(|std_bitset|_\<N + 1>&&)
    {
        return passed_by_rvalue_reference;
    }
};

Named parameters are required when invoking the constructor; however, none of their tags need to be in the same namespace.

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\((_lrc, kw0) in(lrc))
|BOOST_PARAMETER_NAME|_\((_lr, kw1) in_out(lr))
|BOOST_PARAMETER_NAME|_\((_rrc, kw2) in(rrc))
|BOOST_PARAMETER_NAME|_\((_rr, kw3) consume(rr))

Unlike |BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR|, this macro doesn't require a base class, only a delegate function to which the generated constructor can pass its |ArgumentPack|.

.. parsed-literal::

struct D
{
    BOOST_PARAMETER_NO_SPEC_NO_BASE_CONSTRUCTOR(D, D::_evaluate)

 private:
    template <typename Args>
    static bool _evaluate(Args const& args)
    {
        BOOST_TEST_EQ(
            passed_by_lvalue_reference_to_const
          , U::evaluate_category<0>(args[_lrc])
        );
        BOOST_TEST_EQ(
            passed_by_lvalue_reference
          , U::evaluate_category<1>(args[_lr])
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference_to_const
          , U::evaluate_category<2>(
                args[_rrc | rvalue_const_bitset<2>()]
            )
        );
        BOOST_TEST_EQ(
            passed_by_rvalue_reference
          , U::evaluate_category<3>(
                args[_rr | rvalue_bitset<3>()]
            )
        );

        return true;
    }
};

To invoke the constructor, bind all its arguments to named parameters.

.. parsed-literal::

D dp0(
    _rr0 = rvalue_bitset<3>()
  , _lrc0 = lvalue_const_bitset<0>()
  , _lr0 = lvalue_bitset<1>()
  , _rrc0 = rvalue_const_bitset<2>()
);
D dp1(
    _lr0 = lvalue_bitset<1>()
  , _lrc0 = lvalue_const_bitset<0>()
);

The |preproc_eval_cat_no_spec_cpp|_ test program demonstrates proper usage of this macro.

Macro parameters:

cls is the name of the enclosing class.
func is a function that takes in the |ArgumentPack|_ that the generated constructor passes on.

Argument specifiers syntax:

None.

Approximate expansion:

.. parsed-literal::

template <
    typename TaggedArg0
  , typename ...TaggedArgs
  , typename = typename |boost_enable_if|_\<
        |are_tagged_arguments|_\<TaggedArg0,TaggedArgs...>
    >::type
>
inline explicit **cls**\ (
    TaggedArg0 const& arg0
  , TaggedArgs const&... args
)
{
    **func**\ (|compose|_\(arg0, args...));
}

.. |BOOST_PARAMETER_NAME| replace:: BOOST_PARAMETER_NAME .. _BOOST_PARAMETER_NAME:

`BOOST_PARAMETER_NAME(name)`

:Defined in: |name_header|_

Declares a tag-type and keyword object.

If name is of the form:

.. parsed-literal::

(*object-name*, *namespace-name*) *qualifier*\ (*tag-name*)

then

:Requires: qualifier is either in, out, in_out, consume, move_from, or forward. :Expands to:

.. parsed-literal::

namespace *namespace-name* {

    struct *tag-name*
    {
        static constexpr char const* keyword_name()
        {
            return ## *tag-name*;
        }

        typedef *unspecified* _;
        typedef *unspecified* _1;
        typedef boost::parameter::*qualifier* ## _reference qualifier;

        // The following definitions are available only when
        // |BOOST_PARAMETER_CAN_USE_MP11|_ is defined.

        template <typename ArgumentPack>
        using binding_fn = typename |binding|_\<
            ArgumentPack
          , *tag-name*
        >::type;

        template <typename ArgumentPack>
        using fn = typename |value_type|_\<ArgumentPack, *tag-name*>::type;
    };
}

|keyword|_\<*tag-namespace*::*tag-name*> const& *object-name*
    = |keyword|_\<*tag-namespace*::*tag-name*>::instance;

Else If name is of the form:

.. parsed-literal::

(*tag-name*, *namespace-name*) *object-name*

then

Treats name as if it were of the form:

.. parsed-literal::

(forward(*tag-name*), *namespace-name*) *object-name*

Else If name is of the form:

.. parsed-literal::

*qualifier*\ (*tag-name*)

then

:Requires: qualifier is either in, out, in_out, consume, move_from, or forward. :Expands to:

.. parsed-literal::

namespace tag {

    struct *tag-name*
    {
        static constexpr char const* keyword_name()
        {
            return ## *tag-name*;
        }

        typedef *unspecified* _;
        typedef *unspecified* _1;
        typedef boost::parameter::*qualifier* ## _reference qualifier;

        // The following definitions are available only when
        // |BOOST_PARAMETER_CAN_USE_MP11|_ is defined.

        template <typename ArgumentPack>
        using binding_fn = typename |binding|_\<
            ArgumentPack
          , *tag-name*
        >::type;

        template <typename ArgumentPack>
        using fn = typename |value_type|_\<ArgumentPack, *tag-name*>::type;
    };
}

|keyword|_\<tag::*tag-name*> const& _ ## *tag-name*
    = |keyword|_\<tag::*tag-name*>::instance;

Else

Treats name as if it were of the form:

.. parsed-literal::

forward(*tag-name*)

.. |BOOST_PARAMETER_NESTED_KEYWORD| replace:: BOOST_PARAMETER_NESTED_KEYWORD .. _BOOST_PARAMETER_NESTED_KEYWORD:

`BOOST_PARAMETER_NESTED_KEYWORD(tag_namespace, name, alias)`

:Defined in: |nested_keyword_header|_

Declares a tag-type, a keyword object, and an alias for that object nested in the tag-type.

If name is of the form:

.. parsed-literal::

*qualifier*\ (*tag-name*)

then

:Requires: qualifier is either in, out, in_out, consume, move_from, or forward.

:Expands to:

.. parsed-literal::

namespace tag {

    struct *tag-name*
    {
        static constexpr char const* keyword_name()
        {
            return ## *tag-name* ## _;
        }

        typedef *unspecified* _;
        typedef *unspecified* _1;
        typedef boost::parameter::*qualifier* ## _reference qualifier;
        static |keyword|_\<*tag-name*> const& *alias*;

        // The following definitions are available only when
        // |BOOST_PARAMETER_CAN_USE_MP11|_ is defined.

        template <typename ArgumentPack>
        using binding_fn = typename |binding|_\<
            ArgumentPack
          , *tag-name*
        >::type;

        template <typename ArgumentPack>
        using fn = typename |value_type|_\<ArgumentPack, *tag-name*>::type;
    };

    |keyword|_\<*tag-name*> const& tag::*tag-name*::*alias*
        = |keyword|_\<*tag-name*>::instance;
}

|keyword|_\<tag::*tag-name*> const& tag::*tag-name*::*name*
    = |keyword|_\<tag::*tag-name*>::instance;

Else

Treats name as if it were of the form:

.. parsed-literal::

forward(*tag-name*)

.. |BOOST_PARAMETER_TEMPLATE_KEYWORD| replace:: BOOST_PARAMETER_TEMPLATE_KEYWORD .. _BOOST_PARAMETER_TEMPLATE_KEYWORD:

`BOOST_PARAMETER_TEMPLATE_KEYWORD(name)`

:Defined in: |template_keyword_header|_ :Included by: |name_header|_ :Expands to:

.. parsed-literal::

namespace tag {

    struct *name*;
}

template <typename T>
struct *name* : |template_keyword|_\<tag:: *name*, T>
{
};

The |function_type_tpl_param_cpp|_ test program demonstrates proper usage of this macro.

.. |BOOST_PARAMETER_FUN| replace:: BOOST_PARAMETER_FUN .. _BOOST_PARAMETER_FUN:

`BOOST_PARAMETER_FUN(r, n, l, h, p)`

.. admonition:: Deprecated

This macro has been deprecated in favor of
``BOOST_PARAMETER_FUNCTION``.

Generates a sequence of forwarding function_ templates named n, with arities ranging from l to h, returning r, and using p to control overload resolution and assign tags to positional arguments.

:Defined in: |macros_header|_ :Requires: l and h are nonnegative integer tokens such that l < h :Expands to:

.. parsed-literal::

template <typename A1, typename A2, …, typename A ## **l**>
r
    name(
        A1 && a1, A2 && a2, …, A ## **l** && a ## **l**
      , typename **p**::match<A1, A2, …, A ## **l**>::type p = **p**\ ()
    )
{
    return **name**\ _with_named_params(
        **p**\ (
            |std_forward|_\<A1>(a1)
          , |std_forward|_\<A2>(a2)
          , …
          , |std_forward|_\<A ## **l**>(a ## **l**)
        )
    );
}

template <
    typename A1
  , typename A2
  , …
  , typename A ## **l**
  , typename A ## |BOOST_PP_INC|_\ (**l**)
>
r
    name(
        A1 && a1, A2 && a2, …, A ## **l** && a ## **l**
      , A ## |BOOST_PP_INC|_\ (**l**) const& a ## |BOOST_PP_INC|_\ (**l**)
      , typename **p**::match<
            A1, A2, …, A ## **l**, A ## |BOOST_PP_INC|_\ (**l**)
        >::type p = **p**\ ()
    )
{
    return **name**\ _with_named_params(
        **p**\ (
            |std_forward|_\<A1>(a1)
          , |std_forward|_\<A2>(a2)
          , …
          , |std_forward|_\<A ## **l**>(a ## **l**)
          , |std_forward|_\<A ## |BOOST_PP_INC|_\ (**l**)>(
                a ## |BOOST_PP_INC|_\ (**l**)
            )
        )
    );
}

:vellipsis:`⋮`

template <typename A1, typename A2, …, typename A ## **h**>
r
    name(
        A1 && a1, A2 && a2, …, A ## **h** && x ## **h**
      , typename **p**::match<A1, A2, …, A ## **h**>::type p = **p**\ ()
    )
{
    return **name**\ _with_named_params(
        **p**\ (
            |std_forward|_\<A1>(a1)
          , |std_forward|_\<A2>(a2)
          , …
          , |std_forward|_\<A ## **h**>(a ## **h**)
        )
    );
}

The |macros_cpp|_ and |macros_eval_cat_cpp|_ test programs demonstrate proper usage of this macro.

.. |BOOST_PARAMETER_KEYWORD| replace:: BOOST_PARAMETER_KEYWORD .. _BOOST_PARAMETER_KEYWORD:

`BOOST_PARAMETER_KEYWORD(n, k)`

.. admonition:: Deprecated

This macro has been deprecated in favor of
``BOOST_PARAMETER_NAME``.

Generates the declaration of a |keyword tag type| named k in namespace n and a corresponding |keyword object| definition in the enclosing namespace.

:Defined in: |keyword_header|_ :Expands to:

.. parsed-literal::

namespace **n** {

    struct **k**
    {
        static constexpr char const* keyword_name()
        {
            return ## *k*;
        }

        typedef *unspecified* _;
        typedef *unspecified* _1;
        typedef boost::parameter::forward_reference qualifier;

        // The following definitions are available only when
        // |BOOST_PARAMETER_CAN_USE_MP11|_ is defined.

        template <typename ArgumentPack>
        using binding_fn = typename |binding|_\<
            ArgumentPack
          , *k*
        >::type;

        template <typename ArgumentPack>
        using fn = typename |value_type|_\<ArgumentPack, *k*>::type;
    };
}

namespace { 

    |keyword|_\<*n*::**k**> const& **k**
        = |keyword|_\<*n*::**k**>::instance;
}

`BOOST_PARAMETER_MATCH(p, a, x)`

Generates a defaulted parameter declaration for a forwarding function_.

:Defined in: |match_header|_ :Requires: a is a Boost.Preprocessor sequence__ of the form

.. parsed-literal::

(A0)(A1)…(A ## *n*)

__ ../../../preprocessor/doc/data.html

:Expands to:

.. parsed-literal::

typename **p**::match<**A0**\ , **A1**\ , …, **A** ## *n*>::type
    **x** = **p**\ ()

Configuration Macros

.. |BOOST_PARAMETER_HAS_PERFECT_FORWARDING| replace:: BOOST_PARAMETER_HAS_PERFECT_FORWARDING .. _BOOST_PARAMETER_HAS_PERFECT_FORWARDING:

`BOOST_PARAMETER_HAS_PERFECT_FORWARDING`

:Defined in: |config_header|_

.. |BOOST_PARAMETER_DISABLE_PERFECT_FORWARDING| replace:: BOOST_PARAMETER_DISABLE_PERFECT_FORWARDING .. _BOOST_PARAMETER_DISABLE_PERFECT_FORWARDING:

`BOOST_PARAMETER_DISABLE_PERFECT_FORWARDING`

It may be necessary to test user code in case perfect forwarding support is unavailable. Users can #define this macro either in their project settings or before including any library header files. Doing so will leave both |BOOST_PARAMETER_HAS_PERFECT_FORWARDING|_ and |BOOST_PARAMETER_CAN_USE_MP11|_ undefined.

.. |BOOST_PARAMETER_CAN_USE_MP11| replace:: BOOST_PARAMETER_CAN_USE_MP11 .. _BOOST_PARAMETER_CAN_USE_MP11:

`BOOST_PARAMETER_CAN_USE_MP11`

.. Admonition:: Usage Note

|Boost_MP11|_ and |Boost_MPL|_ are **not** mutually exclusive.  It's
perfectly acceptable to specify deduced parameters using both quoted
metafunctions and metafunction classes, for example.  See
|evaluate_category_cpp|_.

:Defined in: |config_header|_ :Example usage:

Given the following definitions:

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\(x)

template <typename A0>
typename |boost_enable_if|_\<|std_is_same|_\<int,A0>,int>::type
    sfinae(A0 const& a0)
{
    return 0;
}

|Boost_MP11|_ allows deduced parameters to be defined more succinctly:

.. parsed-literal::

template <typename T, typename Args>
using predicate = |std_is_convertible|_\<T,char const*>;

|BOOST_PARAMETER_FUNCTION|_\((int), sfinae, tag,
    (deduced
        (optional
            (x
              , \*(|mp11_quote|_\<predicate>)
              , static_cast<char const*>(|std_nullptr|_\)
            )
        )
    )
)
{
    return 1;
}

Without |Boost_MP11|_, deduced parameter definitions tend to be more verbose:

.. parsed-literal::

struct predicate
{
    template <typename T, typename Args>
    struct apply
      : |mpl_if|_\<
            |boost_is_convertible|_\<T,char const*>
          , |mpl_true|_\   // Still have to convert to a
          , |mpl_false|_\  // `Boolean Integral Constant`_.
        >
    {
    };
};

|BOOST_PARAMETER_FUNCTION|_\((int), sfinae, tag,
    (deduced
        (optional
            (x
              , \*(predicate)
              , static_cast<char const*>(|std_nullptr|_\)
            )
        )
    )
)
{
    return 1;
}

Either way, the following assertions will succeed:

.. parsed-literal::

assert(1 == sfinae());
assert(1 == sfinae("foo"));
assert(0 == sfinae(1));

As another example, given the following declarations and definitions:

.. parsed-literal::

|BOOST_PARAMETER_NAME|_\(x)
|BOOST_PARAMETER_NAME|_\(y)

template <typename E, typename Args>
void check0(E const& e, Args const& args);

template <typename P, typename E, typename ...Args>
void check(E const& e, Args const&... args)
{
    check0(e, P()(args...));
}

Argument packs qualify as |Boost_MP11|_-style lists containing |keyword tag type|\ s:

.. parsed-literal::

template <typename Args>
struct some_functor
{
    template <typename K>
    void operator()(K&&) const
    {
        // K is one of tag\:\:x, tag\:\:y, etc.
    }
};

template <typename E, typename Args>
void check0(E const& e, Args const& args)
{
    boost::mp11::mp_for_each<E>(some_functor<Args>());
}

The first check determines whether or not the argument type of _y is the same as the reference type of _x, while the second check determines whether or not the argument type of _y is convertible to the value type of _x. Here, it's possible to access the reference and value result types of indexing an argument pack a little more directly:

.. parsed-literal::

// Use mp_bind on tag\:\:x\:\:binding_fn to access the reference type of _x.
check<
    |parameters|_\<
        tag\:\:x
      , |optional|_\<
            |deduced|_\<tag\:\:y>
          , |mp11_bind|_\<
                |std_is_same|_\  // |boost_is_same|_, standard version.
              , |mp11_1|_\  // will be bound to the argument type of _y.
              , |mp11_bind|_\<
                    tag\:\:x\:\:binding_fn
                  , |mp11_2|_\  // will be bound to the argument pack type.
                >
            >
        >
    >
>((_x = 0, _y = 1), 0, 1);

// Use mp_bind_q on tag\:\:x to access the value type of _x.
check<
    |parameters|_\<
        tag\:\:x
      , |optional|_\<
            |deduced|_\<tag\:\:y>
          , |mp11_bind|_\<
                |std_is_convertible|_\  // |boost_is_convertible|_, standard version.
              , |mp11_1|_\  // will be bound to the argument type of _y.
              , |mp11_bind_q|_\<
                    tag\:\:x
                  , |mp11_2|_\  // will be bound to the argument pack type.
                >
            >
        >
    >
>((_x = 0U, _y = 1U), 0U, 1U);

Argument packs still qualify as |Boost_MPL|_-style lists containing |keyword tag type|\ s:

.. parsed-literal::

template <typename Args>
struct some_functor
{
    template <typename K>
    void operator()(K) const
    {
        // K is one of tag\:\:x, tag\:\:y, etc.
    }
};

template <typename E, typename Args>
void check0(E const& e, Args const& args)
{
    boost::mpl::for_each<E>(some_functor<Args>());
}

However, without |Boost_MP11|_, the corresponding checks become a little more verbose:

.. parsed-literal::

check<
    |parameters|_\<
        tag\:\:x
      , |optional|_\<
            |deduced|_\<tag\:\:y>
          , |mpl_if|_\<
                |boost_is_same|_\<
                    |boost_add_lvalue_reference|_\<|mp11_1|_\>
                  , |binding|_\<|mp11_2|_\, tag\:\:x>
                >
              , |mpl_true|_\   // Still have to convert to a
              , |mpl_false|_\  // `Boolean Integral Constant`_.
            >
        >
    >
>((_x = 0, _y = 1), 0, 1);

// Use tag\:\:x\:\:_ or tag\:\:x\:\:_1 to access the value type of _x.
check<
    |parameters|_\<
        tag\:\:x
      , |optional|_\<
            |deduced|_\<tag\:\:y>
          , |mpl_if|_\<
                |boost_is_convertible|_\<|mp11_1|_\, tag\:\:x\:\:_1>
              , |mpl_true|_\   // Still have to convert to a
              , |mpl_false|_\  // `Boolean Integral Constant`_.
            >
        >
    >
>((_x = 0U, _y = 1U), 0U, 1U);

The |singular_cpp|, |compose_cpp|, |optional_deduced_sfinae_cpp|, and |deduced_dep_pred_cpp| test programs demonstrate proper usage of this macro.

.. |BOOST_PARAMETER_DISABLE_MP11_USAGE| replace:: BOOST_PARAMETER_DISABLE_MP11_USAGE .. _BOOST_PARAMETER_DISABLE_MP11_USAGE:

`BOOST_PARAMETER_DISABLE_MP11_USAGE`

It may be necessary to disable usage of |Boost_MP11|_ for compilers that cannot support it. Users can #define this macro either in their project settings or before including any library header files. Doing so will leave |BOOST_PARAMETER_CAN_USE_MP11|_ undefined.

.. |BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE| replace:: BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE .. _BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE:

`BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE`

:Example:

.. parsed-literal::

#define BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE |fusion_vector|_

:Defined in: |parameters_header|_

.. |BOOST_PARAMETER_MAX_ARITY| replace:: BOOST_PARAMETER_MAX_ARITY .. _BOOST_PARAMETER_MAX_ARITY:

`BOOST_PARAMETER_MAX_ARITY`

If |BOOST_PARAMETER_HAS_PERFECT_FORWARDING|_ is #defined, then:

If the MPL Variadic Sequence_ underlying the nested parameter_spec type of |parameters| does not have a size limit--which is the case with |mp11_list|, |fusion_list|, and |fusion_deque|, but not |mpl_vector|--then this macro can be safely ignored. User code that manually defines |BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE|_ should also manually define this macro to the size limit of the sequence if it has one.

If |BOOST_PARAMETER_HAS_PERFECT_FORWARDING|_ is not #defined, then:

Mutable references must be wrapped by |boost_ref|_ or |std_ref|_ if passed by position to Boost.Parameter-enabled functions with arity greater than or equal to |BOOST_PARAMETER_EXPONENTIAL_OVERLOAD_THRESHOLD_ARITY|_.

.. |BOOST_PARAMETER_COMPOSE_MAX_ARITY| replace:: BOOST_PARAMETER_COMPOSE_MAX_ARITY .. _BOOST_PARAMETER_COMPOSE_MAX_ARITY:

`BOOST_PARAMETER_COMPOSE_MAX_ARITY`

:Defined in: |config_header|_ :Default Value: 20 for a few older compilers, 64 otherwise :Minimum Value: 2

.. |BOOST_PARAMETER_EXPONENTIAL_OVERLOAD_THRESHOLD_ARITY| replace:: BOOST_PARAMETER_EXPONENTIAL_OVERLOAD_THRESHOLD_ARITY .. _BOOST_PARAMETER_EXPONENTIAL_OVERLOAD_THRESHOLD_ARITY:

`BOOST_PARAMETER_EXPONENTIAL_OVERLOAD_THRESHOLD_ARITY`

If this library does not support perfect forwarding, determines the number of arguments less than which |parameters| generates an exponential number of function call operator overloads, and greater than or equal to which |parameters| does not. Will only be #defined by the library if it is not already #defined and |BOOST_PARAMETER_HAS_PERFECT_FORWARDING|_ is not #defined.

:Defined in: |config_header|_ :Default Value: 0 :Minimum Value: 0

...Outside Of This Library

Tutorial

Follow this link__ to the Boost.Parameter tutorial documentation.

__ index.html#tutorial

//////////////////////////////////////////////////////////////////////////////

.. [#thread] References to tag objects may be initialized multiple times. This scenario can only occur in the presence of threading. Because the C++ standard doesn't consider threading, it doesn't explicitly allow or forbid multiple initialization of references. That said, it's hard to imagine an implementation where it could make a difference.

.. [#no_result_of] Where |BOOST_NO_RESULT_OF|_ is #defined, |boost_result_of|_\ <F()>::type is replaced by F::result_type.

.. |std_nullptr| replace:: std::nullptr .. _std_nullptr: http://en.cppreference.com/w/cpp/language/nullptr .. |std_forward| replace:: std::forward .. _std_forward: http://en.cppreference.com/w/cpp/utility/forward .. |std_enable_if| replace:: std::enable_if .. _std_enable_if: http://en.cppreference.com/w/cpp/types/enable_if .. |std_is_convertible| replace:: std::is_convertible .. _std_is_convertible: http://en.cppreference.com/w/cpp/types/is_convertible .. |std_is_same| replace:: std::is_same .. _std_is_same: http://en.cppreference.com/w/cpp/types/is_same .. |std_ref| replace:: std::ref .. _std_ref: http://en.cppreference.com/w/cpp/utility/functional/ref .. |std_map| replace:: std::map .. _std_map: http://en.cppreference.com/w/cpp/container/map .. |std_string| replace:: std::string .. _std_string: http://en.cppreference.com/w/cpp/string/basic_string .. |std_bitset| replace:: std::bitset .. _std_bitset: http://en.cppreference.com/w/cpp/utility/bitset .. |Boost_Config| replace:: Boost.Config .. _Boost_Config: ../../../config/doc/html/index.html .. |BOOST_NO_FUNCTION_TEMPLATE_ORDERING| replace:: BOOST_NO_FUNCTION_TEMPLATE_ORDERING .. _BOOST_NO_FUNCTION_TEMPLATE_ORDERING: ../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__03_defects .. |BOOST_NO_SFINAE| replace:: BOOST_NO_SFINAE .. _BOOST_NO_SFINAE: ../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__03_defects .. |BOOST_NO_CXX11_AUTO_DECLARATIONS| replace:: BOOST_NO_CXX11_AUTO_DECLARATIONS .. _BOOST_NO_CXX11_AUTO_DECLARATIONS: ../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported .. |BOOST_NO_CXX11_CONSTEXPR| replace:: BOOST_NO_CXX11_CONSTEXPR .. _BOOST_NO_CXX11_CONSTEXPR: ../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported .. |BOOST_NO_CXX11_DECLTYPE_N3276| replace:: BOOST_NO_CXX11_DECLTYPE_N3276 .. _BOOST_NO_CXX11_DECLTYPE_N3276: ../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported .. |BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS| replace:: BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS .. _BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS: ../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported .. |BOOST_NO_CXX11_HDR_INITIALIZER_LIST| replace:: BOOST_NO_CXX11_HDR_INITIALIZER_LIST .. _BOOST_NO_CXX11_HDR_INITIALIZER_LIST: ../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported .. |BOOST_NO_CXX11_HDR_TUPLE| replace:: BOOST_NO_CXX11_HDR_TUPLE .. _BOOST_NO_CXX11_HDR_TUPLE: ../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported .. |BOOST_NO_CXX11_HDR_TYPE_TRAITS| replace:: BOOST_NO_CXX11_HDR_TYPE_TRAITS .. _BOOST_NO_CXX11_HDR_TYPE_TRAITS: ../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported .. |BOOST_NO_CXX11_RVALUE_REFERENCES| replace:: BOOST_NO_CXX11_RVALUE_REFERENCES .. _BOOST_NO_CXX11_RVALUE_REFERENCES: ../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported .. |BOOST_NO_CXX11_STATIC_ASSERT| replace:: BOOST_NO_CXX11_STATIC_ASSERT .. _BOOST_NO_CXX11_STATIC_ASSERT: ../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported .. |BOOST_NO_CXX11_TEMPLATE_ALIASES| replace:: BOOST_NO_CXX11_TEMPLATE_ALIASES .. _BOOST_NO_CXX11_TEMPLATE_ALIASES: ../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported .. |BOOST_NO_CXX11_VARIADIC_TEMPLATES| replace:: BOOST_NO_CXX11_VARIADIC_TEMPLATES .. _BOOST_NO_CXX11_VARIADIC_TEMPLATES: ../../../config/doc/html/boost_config/boost_macro_reference.html#boost_config.boost_macro_reference.macros_that_describe_c__11_features_not_supported .. |Boost_Preprocessor| replace:: Boost.Preprocessor .. _Boost_Preprocessor: ../../../preprocessor/doc/index.html .. _sequence: ../../../preprocessor/doc/data/sequences.html .. |BOOST_PP_INC| replace:: BOOST_PP_INC .. _BOOST_PP_INC: ../../../preprocessor/doc/ref/inc.html .. |boost_enable_if| replace:: boost::enable_if .. _boost_enable_if: ../../../core/doc/html/core/enable_if.html .. |boost_enable_if_c| replace:: boost::enable_if_c .. _boost_enable_if_c: ../../../core/doc/html/core/enable_if.html .. |boost_lazy_enable_if| replace:: boost::lazy_enable_if .. _boost_lazy_enable_if: ../../../core/doc/html/core/enable_if.html .. |boost_lazy_enable_if_c| replace:: boost::lazy_enable_if_c .. _boost_lazy_enable_if_c: ../../../core/doc/html/core/enable_if.html .. |boost_disable_if| replace:: boost::disable_if .. _boost_disable_if: ../../../core/doc/html/core/enable_if.html .. |boost_disable_if_c| replace:: boost::disable_if_c .. _boost_disable_if_c: ../../../core/doc/html/core/enable_if.html .. |boost_lazy_disable_if| replace:: boost::lazy_disable_if .. _boost_lazy_disable_if: ../../../core/doc/html/core/enable_if.html .. |boost_lazy_disable_if_c| replace:: boost::lazy_disable_if_c .. _boost_lazy_disable_if_c: ../../../core/doc/html/core/enable_if.html .. |boost_ref| replace:: boost::ref .. _boost_ref: ../../../core/doc/html/core/ref.html .. |BOOST_NO_RESULT_OF| replace:: BOOST_NO_RESULT_OF .. _BOOST_NO_RESULT_OF: ../../../utility/utility.htm#BOOST_NO_RESULT_OF .. |boost_result_of| replace:: boost::result_of .. _boost_result_of: ../../../utility/utility.htm#result_of .. |boost_is_const| replace:: boost::is_const .. _boost_is_const: ../../../type_traits/doc/html/boost_typetraits/is_const.html .. |boost_is_convertible| replace:: boost::is_convertible .. _boost_is_convertible: ../../../type_traits/doc/html/boost_typetraits/is_convertible.html .. |boost_is_same| replace:: boost::is_same .. _boost_is_same: ../../../type_traits/doc/html/boost_typetraits/is_same.html .. |boost_is_scalar| replace:: boost::is_scalar .. _boost_is_scalar: ../../../type_traits/doc/html/boost_typetraits/is_scalar.html .. |boost_add_lvalue_reference| replace:: boost::add_lvalue_reference .. _boost_add_lvalue_reference: ../../../type_traits/doc/html/boost_typetraits/add_lvalue_reference.html .. |boost_remove_reference| replace:: boost::remove_reference .. _boost_remove_reference: ../../../type_traits/doc/html/boost_typetraits/remove_reference.html .. |Boost_MPL| replace:: Boost.MPL .. _Boost_MPL: ../../../mpl/doc/index.html .. _Metafunction: ../../../mpl/doc/refmanual/metafunction.html .. _Boolean Integral Constant: ../../../mpl/doc/refmanual/integral-constant.html .. _MPL Binary Metafunction Class: ../../../mpl/doc/refmanual/metafunction-class.html .. _MPL Forward Sequence: ../../../mpl/doc/refmanual/forward-sequence.html .. _MPL Associative Sequence: ../../../mpl/doc/refmanual/associative-sequence.html .. _MPL Variadic Sequence: ../../../mpl/doc/refmanual/variadic-sequence.html .. |BOOST_MPL_LIMIT_VECTOR_SIZE| replace:: BOOST_MPL_LIMIT_VECTOR_SIZE .. _BOOST_MPL_LIMIT_VECTOR_SIZE: ../../../mpl/doc/refmanual/limit-vector-size.html .. |mpl_eval_if| replace:: boost::mpl::eval_if .. _mpl_eval_if: ../../../mpl/doc/refmanual/eval-if.html .. |mpl_true| replace:: mpl::true_ .. _mpl_true: ../../../mpl/doc/refmanual/bool.html .. |mpl_false| replace:: mpl::false_ .. _mpl_false: ../../../mpl/doc/refmanual/bool.html .. |mpl_if| replace:: mpl::if_ .. _mpl_if: ../../../mpl/doc/refmanual/if.html .. |mpl_vector| replace:: boost::mpl::vector .. _mpl_vector: ../../../mpl/doc/refmanual/vector.html .. |Boost_MP11| replace:: Boost.MP11 .. _Boost_MP11: ../../../mp11/doc/html/mp11.html .. |mp11_quote| replace:: boost::mp11::mp_quote .. _mp11_quote: ../../../mp11/doc/html/mp11.html#mp_quotef .. |mp11_1| replace:: boost::mp11::_1 .. _mp11_1: ../../../mp11/doc/html/mp11.html#1_9 .. |mp11_2| replace:: boost::mp11::_2 .. _mp11_2: ../../../mp11/doc/html/mp11.html#1_9 .. |mp11_bind| replace:: boost::mp11::mp_bind .. _mp11_bind: ../../../mp11/doc/html/mp11.html#mp_bindf_t .. |mp11_bind_q| replace:: boost::mp11::mp_bind_q .. _mp11_bind_q: ../../../mp11/doc/html/mp11.html#mp_bind_qq_t .. |mp11_list| replace:: boost::mp11::mp_list .. _mp11_list: ../../../mp11/doc/html/mp11.html#mp_listt .. |Boost_Fusion| replace:: Boost.Fusion .. _Boost_Fusion: ../../../fusion/doc/html/index.html .. |BOOST_FUSION_HAS_VARIADIC_DEQUE| replace:: BOOST_FUSION_HAS_VARIADIC_DEQUE .. _BOOST_FUSION_HAS_VARIADIC_DEQUE: ../../../../boost/fusion/container/deque/deque_fwd.hpp .. |BOOST_FUSION_HAS_VARIADIC_LIST| replace:: BOOST_FUSION_HAS_VARIADIC_LIST .. _BOOST_FUSION_HAS_VARIADIC_LIST: ../../../../boost/fusion/container/list/list_fwd.hpp .. |fusion_vector| replace:: boost::fusion::vector .. _fusion_vector: ../../../fusion/doc/html/fusion/container/vector.html .. |fusion_deque| replace:: boost::fusion::deque .. _fusion_deque: ../../../fusion/doc/html/fusion/container/deque.html .. |fusion_list| replace:: boost::fusion::list .. _fusion_list: ../../../fusion/doc/html/fusion/container/list.html .. |config_header| replace:: boost/parameter/config.hpp .. _config_header: ../../../../boost/parameter/config.hpp .. |binding_header| replace:: boost/parameter/binding.hpp .. _binding_header: ../../../../boost/parameter/binding.hpp .. |value_type_header| replace:: boost/parameter/value_type.hpp .. _value_type_header: ../../../../boost/parameter/value_type.hpp .. |are_tagged_arguments_header| replace:: boost/parameter/are_tagged_arguments.hpp .. _are_tagged_arguments_header: ../../../../boost/parameter/are_tagged_arguments.hpp .. |is_argument_pack_header| replace:: boost/parameter/is_argument_pack.hpp .. _is_argument_pack_header: ../../../../boost/parameter/is_argument_pack.hpp .. |template_keyword_header| replace:: boost/parameter/template_keyword.hpp .. _template_keyword_header: ../../../../boost/parameter/template_keyword.hpp .. |keyword_header| replace:: boost/parameter/keyword.hpp .. _keyword_header: ../../../../boost/parameter/keyword.hpp .. |name_header| replace:: boost/parameter/name.hpp .. _name_header: ../../../../boost/parameter/name.hpp .. |nested_keyword_header| replace:: boost/parameter/nested_keyword.hpp .. _nested_keyword_header: ../../../../boost/parameter/nested_keyword.hpp .. |compose_header| replace:: boost/parameter/compose.hpp .. _compose_header: ../../../../boost/parameter/compose.hpp .. |preprocessor_no_spec_header| replace:: boost/parameter/preprocessor_no_spec.hpp .. _preprocessor_no_spec_header: ../../../../boost/parameter/preprocessor_no_spec.hpp .. |required_header| replace:: boost/parameter/required.hpp .. _required_header: ../../../../boost/parameter/required.hpp .. |optional_header| replace:: boost/parameter/optional.hpp .. _optional_header: ../../../../boost/parameter/optional.hpp .. |deduced_header| replace:: boost/parameter/deduced.hpp .. _deduced_header: ../../../../boost/parameter/deduced.hpp .. |parameters_header| replace:: boost/parameter/parameters.hpp .. _parameters_header: ../../../../boost/parameter/parameters.hpp .. |match_header| replace:: boost/parameter/match.hpp .. _match_header: ../../../../boost/parameter/match.hpp .. |macros_header| replace:: boost/parameter/macros.hpp .. _macros_header: ../../../../boost/parameter/macros.hpp .. |preprocessor_header| replace:: boost/parameter/preprocessor.hpp .. _preprocessor_header: ../../../../boost/parameter/preprocessor.hpp .. |function_type_tpl_param_cpp| replace:: function_type_tpl_param.cpp .. _function_type_tpl_param_cpp: ../../test/function_type_tpl_param.cpp .. |ntp_cpp| replace:: test/ntp.cpp .. _ntp_cpp: ../../test/ntp.cpp .. |singular_cpp| replace:: singular.cpp .. _singular_cpp: ../../test/singular.cpp .. |compose_cpp| replace:: compose.cpp .. _compose_cpp: ../../test/compose.cpp .. |evaluate_category_cpp| replace:: evaluate_category.cpp .. _evaluate_category_cpp: ../../test/evaluate_category.cpp .. |parameterized_inheritance_cpp| replace:: parameterized_inheritance.cpp .. _parameterized_inheritance_cpp: ../../test/parameterized_inheritance.cpp .. |preproc_eval_cat_no_spec_cpp| replace:: preprocessor_eval_cat_no_spec.cpp .. _preproc_eval_cat_no_spec_cpp: ../../test/preprocessor_eval_cat_no_spec.cpp .. |preprocessor_eval_cat_cpp| replace:: preprocessor_eval_category.cpp .. _preprocessor_eval_cat_cpp: ../../test/preprocessor_eval_category.cpp .. |preprocessor_eval_cat_8_cpp| replace:: preprocessor_eval_cat_8.cpp .. _preprocessor_eval_cat_8_cpp: ../../test/preprocessor_eval_cat_8.cpp .. |optional_deduced_sfinae_cpp| replace:: optional_deduced_sfinae.cpp .. _optional_deduced_sfinae_cpp: ../../test/optional_deduced_sfinae.cpp .. |mpl_cpp| replace:: mpl.cpp .. _mpl_cpp: ../../test/mpl.cpp .. |preprocessor_cpp| replace:: preprocessor.cpp .. _preprocessor_cpp: ../../test/preprocessor.cpp .. |preprocessor_deduced_cpp| replace:: preprocessor_deduced.cpp .. _preprocessor_deduced_cpp: ../../test/preprocessor_deduced.cpp .. |deduced_dep_pred_cpp| replace:: deduced_dependent_predicate.cpp .. _deduced_dep_pred_cpp: ../../test/deduced_dependent_predicate.cpp .. |macros_eval_cat_cpp| replace:: macros_eval_category.cpp .. _macros_eval_cat_cpp: ../../test/macros_eval_category.cpp .. |macros_cpp| replace:: macros.cpp .. _macros_cpp: ../../test/macros.cpp

The Boost Parameter Library Reference Documentation

Preliminaries

Namespaces

Exceptions

Thread Safety

Typography

Terminology

Concepts

|ArgumentPack|

|ParameterSpec|

Class Templates

keyword

template_keyword

parameters

optional, required

deduced

Metafunctions

binding

lazy_binding

value_type

lazy_value_type

are_tagged_arguments

is_argument_pack

result_of::compose

Function Templates

compose

Code Generation Macros

BOOST_PARAMETER_FUNCTION(result, name, tag_namespace, arguments)

BOOST_PARAMETER_MEMBER_FUNCTION(result, name, tag_namespace, arguments)

BOOST_PARAMETER_CONST_MEMBER_FUNCTION(result, name, tag_ns, arguments)

BOOST_PARAMETER_FUNCTION_CALL_OPERATOR(result, tag_namespace, arguments)

BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR(result, tag_ns, arguments)

BOOST_PARAMETER_CONSTRUCTOR(cls, impl, tag_namespace, arguments)

BOOST_PARAMETER_BASIC_FUNCTION(result, name, tag_namespace, arguments)

BOOST_PARAMETER_BASIC_MEMBER_FUNCTION(result, name, tag_ns, arguments)

BOOST_PARAMETER_BASIC_CONST_MEMBER_FUNCTION(result, name, tag_ns, args)

BOOST_PARAMETER_BASIC_FUNCTION_CALL_OPERATOR(result, tag_ns, arguments)

BOOST_PARAMETER_BASIC_CONST_FUNCTION_CALL_OPERATOR(result, tag_ns, args)

BOOST_PARAMETER_NO_SPEC_FUNCTION(result, name)

BOOST_PARAMETER_NO_SPEC_MEMBER_FUNCTION(result, name)

BOOST_PARAMETER_NO_SPEC_CONST_MEMBER_FUNCTION(result, name)

BOOST_PARAMETER_NO_SPEC_FUNCTION_CALL_OPERATOR(result)

BOOST_PARAMETER_NO_SPEC_CONST_FUNCTION_CALL_OPERATOR(result)

BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR(cls, impl)

BOOST_PARAMETER_NO_SPEC_NO_BASE_CONSTRUCTOR(cls, impl)

BOOST_PARAMETER_NAME(name)

BOOST_PARAMETER_NESTED_KEYWORD(tag_namespace, name, alias)

BOOST_PARAMETER_TEMPLATE_KEYWORD(name)

BOOST_PARAMETER_FUN(r, n, l, h, p)

BOOST_PARAMETER_KEYWORD(n, k)

BOOST_PARAMETER_MATCH(p, a, x)

Configuration Macros

BOOST_PARAMETER_HAS_PERFECT_FORWARDING

BOOST_PARAMETER_DISABLE_PERFECT_FORWARDING

BOOST_PARAMETER_CAN_USE_MP11

BOOST_PARAMETER_DISABLE_MP11_USAGE

BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE

BOOST_PARAMETER_MAX_ARITY

BOOST_PARAMETER_COMPOSE_MAX_ARITY

BOOST_PARAMETER_EXPONENTIAL_OVERLOAD_THRESHOLD_ARITY

...Outside Of This Library

Tutorial

`keyword`

`template_keyword`

`parameters`

`optional`, `required`

`deduced`

`binding`

`lazy_binding`

`value_type`

`lazy_value_type`

`are_tagged_arguments`

`is_argument_pack`

`result_of::compose`

`compose`

`BOOST_PARAMETER_FUNCTION(result, name, tag_namespace, arguments)`

`BOOST_PARAMETER_MEMBER_FUNCTION(result, name, tag_namespace, arguments)`

`BOOST_PARAMETER_CONST_MEMBER_FUNCTION(result, name, tag_ns, arguments)`

`BOOST_PARAMETER_FUNCTION_CALL_OPERATOR(result, tag_namespace, arguments)`

`BOOST_PARAMETER_CONST_FUNCTION_CALL_OPERATOR(result, tag_ns, arguments)`

`BOOST_PARAMETER_CONSTRUCTOR(cls, impl, tag_namespace, arguments)`

`BOOST_PARAMETER_BASIC_FUNCTION(result, name, tag_namespace, arguments)`

`BOOST_PARAMETER_BASIC_MEMBER_FUNCTION(result, name, tag_ns, arguments)`

`BOOST_PARAMETER_BASIC_CONST_MEMBER_FUNCTION(result, name, tag_ns, args)`

`BOOST_PARAMETER_BASIC_FUNCTION_CALL_OPERATOR(result, tag_ns, arguments)`

`BOOST_PARAMETER_BASIC_CONST_FUNCTION_CALL_OPERATOR(result, tag_ns, args)`

`BOOST_PARAMETER_NO_SPEC_FUNCTION(result, name)`

`BOOST_PARAMETER_NO_SPEC_MEMBER_FUNCTION(result, name)`

`BOOST_PARAMETER_NO_SPEC_CONST_MEMBER_FUNCTION(result, name)`

`BOOST_PARAMETER_NO_SPEC_FUNCTION_CALL_OPERATOR(result)`

`BOOST_PARAMETER_NO_SPEC_CONST_FUNCTION_CALL_OPERATOR(result)`

`BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR(cls, impl)`

`BOOST_PARAMETER_NO_SPEC_NO_BASE_CONSTRUCTOR(cls, impl)`

`BOOST_PARAMETER_NAME(name)`

`BOOST_PARAMETER_NESTED_KEYWORD(tag_namespace, name, alias)`

`BOOST_PARAMETER_TEMPLATE_KEYWORD(name)`

`BOOST_PARAMETER_FUN(r, n, l, h, p)`

`BOOST_PARAMETER_KEYWORD(n, k)`

`BOOST_PARAMETER_MATCH(p, a, x)`

`BOOST_PARAMETER_HAS_PERFECT_FORWARDING`

`BOOST_PARAMETER_DISABLE_PERFECT_FORWARDING`

`BOOST_PARAMETER_CAN_USE_MP11`

`BOOST_PARAMETER_DISABLE_MP11_USAGE`

`BOOST_PARAMETER_VARIADIC_MPL_SEQUENCE`

`BOOST_PARAMETER_MAX_ARITY`

`BOOST_PARAMETER_COMPOSE_MAX_ARITY`

`BOOST_PARAMETER_EXPONENTIAL_OVERLOAD_THRESHOLD_ARITY`