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BOOST_MPL_ASSERT_MSG

Synopsis

#define BOOST_MPL_ASSERT_MSG( condition, message, types ) \
    unspecified token sequence \
/**/

Description

Generates a compilation error with an embedded custom message when the condition doesn't hold.

Header

#include <boost/mpl/assert.hpp>

Parameters

Parameter Requirement Description
condition An integral constant expression A condition to be asserted.
message A legal identifier token A custom message in a form of a legal C++ identifier token.
types A legal function parameter list A parenthized list of types to be displayed in the error message.

Expression semantics

For any integral constant expression expr, legal C++ identifier message, and arbitrary types t1, t2,... tn:

BOOST_MPL_ASSERT_MSG( expr, message, (t1, t2,... tn) );
Return type:None.
Precondition:t1, t2,... tn are non-void.
Semantics:

Generates a compilation error if expr::value != true, otherwise has no effect.

When possible within the compiler's diagnostic capabilities, the error message will include the message identifier and the parenthized list of t1, t2,... tn types, and have a general form of:

... ************( ...::message )************)(t1, t2,... tn) ...
BOOST_MPL_ASSERT_MSG( expr, message, (types<t1, t2,... tn>) );
Return type:None.
Precondition:None.
Semantics:

Generates a compilation error if expr::value != true, otherwise has no effect.

When possible within the compiler's diagnostics capabilities, the error message will include the message identifier and the list of t1, t2,... tn types, and have a general form of:

... ************( ...::message )************)(types<t1, t2,... tn>) ...

Example

template< typename T > struct my
{
    // ...
    BOOST_MPL_ASSERT_MSG( 
          is_integral<T>::value
        , NON_INTEGRAL_TYPES_ARE_NOT_ALLOWED
        , (T)
        );
};

my<void*> test;

// In instantiation of `my<void*>':
//   instantiated from here
// conversion from `
//   mpl_::failed************(my<void*>::
//   NON_INTEGRAL_TYPES_ARE_NOT_ALLOWED::************)(void*)
//   ' to non-scalar type `mpl_::assert<false>' requested

See also

Asserts, BOOST_MPL_ASSERT, BOOST_MPL_ASSERT_NOT, BOOST_MPL_ASSERT_RELATION