.. Sequences/Concepts//Variadic Sequence |100

Variadic Sequence

Description

A |Variadic Sequence| is a member of a family of sequence classes with both variadic and numbered forms. If seq is a generic name for some |Variadic Sequence|, its variadic form allows us to specify a sequence of n elements |t1...tn|, for any n from 0 up to a preprocessor-configurable limit__ BOOST_MPL_LIMIT_\ seq\ _SIZE, using the following notation:

__ Configuration_

.. line-block::

    ``seq<``\ |t1...tn|\ ``>``

By contrast, each numbered sequence form accepts the exact number of elements that is encoded in the name of the corresponding class template:

.. line-block::

    ``seq``\ *n*\ ``<``\ |t1...tn|\ ``>``

For numbered forms, there is no predefined top limit for n, aside from compiler limitations on the number of template parameters.

.. The variadic form of sequence seq is defined in <boost/mpl/\ seq\ .hpp> header. The numbered forms are defined in batches of 10.

Expression requirements

|In the following table...| seq is a placeholder token for the actual |Variadic Sequence| name.

.. |seq<t1...tn>| replace:: seq<\ |t1...tn|\ > .. |seq<t1...tn>::type| replace:: seq<\ |t1...tn|\ >::type

.. |seqn<t1...tn>| replace:: seq\ n\ <\ |t1...tn|\ > .. |seqn<t1...tn>::type| replace:: seq\ n\ <\ |t1...tn|\ >::type

+---------------------------+-----------------------+---------------------------+ | Expression | Type | Complexity | +===========================+=======================+===========================+ | |seq<t1...tn>| | |Forward Sequence| | Amortized constant time | +---------------------------+-----------------------+---------------------------+ | |seq<t1...tn>::type| | |Forward Sequence| | Amortized constant time | +---------------------------+-----------------------+---------------------------+ | |seqn<t1...tn>| | |Forward Sequence| | Amortized constant time | +---------------------------+-----------------------+---------------------------+ | |seqn<t1...tn>::type| | |Forward Sequence| | Amortized constant time | +---------------------------+-----------------------+---------------------------+

Expression semantics

.. parsed-literal::

typedef seq<|t1...tn|> s;
typedef seq\ *n*\ <|t1...tn|> s;

:Semantics: s is a sequence of elements |t1...tn|.

:Postcondition: size<s>::value == n.

.. FIXME .. parsed-literal::

    BOOST_MPL_ASSERT((|is_same|\< at_c<v,0>::type,\ |t1| >));
    BOOST_MPL_ASSERT((|is_same|\< at_c<v,1>::type,\ |t2| >));
    ...
    BOOST_MPL_ASSERT((|is_same|\< at_c<v,\ *n*>::type,\ |tn| >));

.. ..........................................................................

.. parsed-literal::

typedef seq<|t1...tn|>::type s;
typedef seq\ *n*\ <|t1...tn|>::type s;

:Semantics: s is identical to seq\ n\ <\ |t1...tn| >.

:Postcondition: size<s>::value == n.

Models

• |vector|
• |list|
• |map|

See also

|Sequences|, |Configuration|, |Integral Sequence Wrapper|

.. |variadic| replace:: variadic_ .. variadic: Variadic Sequence

.. |variadic forms| replace:: variadic forms_ .. variadic forms: Variadic Sequence

.. |numbered forms| replace:: numbered forms_ .. numbered forms: Variadic Sequence

.. copyright:: Copyright 2001-2009 Aleksey Gurtovoy and David Abrahams 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)