.. Macros/Asserts//BOOST_MPL_ASSERT

BOOST_MPL_ASSERT

Synopsis

.. parsed-literal::

#define BOOST_MPL_ASSERT( pred ) \\
    |unspecified-token-seq| \\
/\*\*/

Description

Generates a compilation error when the predicate pred holds false.

Header

.. parsed-literal::

#include <boost/mpl/assert.hpp>

Parameters

+---------------+-----------------------------------+-------------------------------+ | Parameter | Requirement | Description | +===============+===================================+===============================+ | pred | Boolean nullary |Metafunction| | A predicate to be asserted. | +---------------+-----------------------------------+-------------------------------+

Expression semantics

For any boolean nullary |Metafunction| pred:

.. parsed-literal::

BOOST_MPL_ASSERT(( pred ));

:Return type: None.

:Semantics: Generates a compilation error if pred::type::value != true, otherwise has no effect. Note that double parentheses are required even if no commas appear in the condition.

When possible within the compiler's diagnostic capabilities,
the error message will include the predicate's full type name, and have a 
general form of:

.. parsed-literal::

   |...| \*\*\*\*\*\*\*\*\*\*\*\* pred::\*\*\*\*\*\*\*\*\*\*\*\* |...|

Example

::

template< typename T, typename U > struct my
{
    // ...
    BOOST_MPL_ASSERT(( is_same< T,U > ));
};

my<void*,char*> test;

// In instantiation of `my<void, char*>':
//   instantiated from here
// conversion from `
//   mpl_::failed************boost::is_same<void, char*>::************' to 
//   non-scalar type `mpl_::assert<false>' requested

See also

|Asserts|, |BOOST_MPL_ASSERT_NOT|, |BOOST_MPL_ASSERT_MSG|, |BOOST_MPL_ASSERT_RELATION|

.. 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)