assert_not.rst

C++的一个好库。。。现在很流行

.. Macros/Asserts//BOOST_MPL_ASSERT_NOT

BOOST_MPL_ASSERT_NOT
====================

Synopsis
--------

.. parsed-literal::
    
    #define BOOST_MPL_ASSERT_NOT( pred ) \\
        |unspecified-token-seq| \\
    /\*\*/


Description
-----------

Generates a compilation error when predicate holds true.


Header
------

.. parsed-literal::
    
    #include <boost/mpl/assert.hpp>


Parameters
----------

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


Expression semantics
--------------------

For any boolean nullary |Metafunction| ``pred``:


.. parsed-literal::

    BOOST_MPL_ASSERT_NOT(( pred ));

:Return type:
    None.

:Semantics:
    Generates a compilation error if ``pred::type::value != false``, 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::
    
        |...| \*\*\*\*\*\*\*\*\*\*\*\*boost::mpl::not_< pred >::\*\*\*\*\*\*\*\*\*\*\*\* |...|


Example
-------

::
    
    template< typename T, typename U > struct my
    {
        // ...
        BOOST_MPL_ASSERT_NOT(( is_same< T,U > ));
    };
    
    my<void,void> test;

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


See also
--------

|Asserts|, |BOOST_MPL_ASSERT|, |BOOST_MPL_ASSERT_MSG|, |BOOST_MPL_ASSERT_RELATION|