dbf9e800
 Hu Chunming
提交_GLIBCXX_USE_CX...
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// (C) Copyright Edward Diener 2011-2015
// Use, modification and distribution are subject to 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).
#if !defined(BOOST_VMD_IDENTITY_HPP)
#define BOOST_VMD_IDENTITY_HPP
#include <boost/vmd/detail/setup.hpp>
#if BOOST_PP_VARIADICS
#if BOOST_VMD_MSVC
#include <boost/preprocessor/cat.hpp>
#endif
#include <boost/vmd/empty.hpp>
/*
The succeeding comments in this file are in doxygen format.
*/
/** \file
*/
/** \def BOOST_VMD_IDENTITY(item)
\brief Macro which expands to its argument when invoked with any number of parameters.
item = any single argument
When BOOST_VMD_IDENTITY(item) is subsequently invoked with any number of parameters it expands
to 'item'. Subsequently invoking the macro is done as 'BOOST_VMD_IDENTITY(item)(zero_or_more_arguments)'.
The macro is equivalent to the Boost PP macro BOOST_PP_IDENTITY(item) with the difference
being that BOOST_PP_IDENTITY(item) is always invoked with no arguments, as in
'BOOST_VMD_IDENTITY(item)()' whereas BOOST_VMD_IDENTITY can be invoked with any number of
arguments.
The macro is meant to be used in BOOST_PP_IF and BOOST_PP_IIF statements when only one
of the clauses needs to be invoked with calling another macro and the other is meant to
return an 'item'.
returns = the macro as 'BOOST_VMD_IDENTITY(item)', when invoked with any number of parameters
as in '(zero_or_more_arguments)', returns 'item'. The macro itself returns
'item BOOST_VMD_EMPTY'.
*/
#define BOOST_VMD_IDENTITY(item) item BOOST_VMD_EMPTY
/** \def BOOST_VMD_IDENTITY_RESULT(result)
\brief Macro which wraps any result which can return its value using BOOST_VMD_IDENTITY or 'item BOOST_VMD_EMPTY'.
result = any single result returned when BOOST_VMD_IDENTITY is used or 'item BOOST_VMD_EMPTY'.
The reason for this macro is to smooth over a problem when using VC++ with BOOST_VMD_IDENTITY.
If your BOOST_VMD_IDENTITY macro can be used where VC++ is the compiler then you need to
surround your macro code which could return a result with this macro in order that VC++ handles
BOOST_VMD_IDENTITY correctly.
If you are not using VC++ you do not have to use this macro, but doing so does no harm.
*/
#if BOOST_VMD_MSVC
#define BOOST_VMD_IDENTITY_RESULT(result) BOOST_PP_CAT(result,)
#else
#define BOOST_VMD_IDENTITY_RESULT(result) result
#endif
#endif /* BOOST_PP_VARIADICS */
#endif /* BOOST_VMD_IDENTITY_HPP */
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