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119 lines
3.4 KiB
119 lines
3.4 KiB
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// (C) Copyright Edward Diener 2011-2015,2019 |
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// Use, modification and distribution are subject to the Boost Software License, |
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// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at |
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// http://www.boost.org/LICENSE_1_0.txt). |
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#if !defined(BOOST_VMD_IS_EMPTY_HPP) |
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#define BOOST_VMD_IS_EMPTY_HPP |
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#include <boost/vmd/detail/setup.hpp> |
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#if BOOST_PP_VARIADICS |
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#include <boost/preprocessor/punctuation/is_begin_parens.hpp> |
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#include <boost/vmd/detail/is_empty.hpp> |
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/* |
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The succeeding comments in this file are in doxygen format. |
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*/ |
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/** \file |
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*/ |
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/** \def BOOST_VMD_IS_EMPTY(...) |
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\brief Tests whether its input is empty or not. |
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The macro checks to see if the input is empty or not. |
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It returns 1 if the input is empty, else returns 0. |
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The macro is a variadic macro taking any input. |
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For the VC++8 compiler (VS2005) the macro takes a single parameter of input to check. |
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For all levels of C++ prior to C++20 the macro is not perfect, |
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and can not be so. The problem area is if the input to be |
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checked is a function-like macro name, in which case either |
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a compiler error can result or a false result can occur. |
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For C++20, with its support for the new __VA_OPT__ preprocessor |
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construct, the macro will always work correctly no matter what |
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the variadic input, and is therefore 100% reliable. |
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This macro is a replacement, using variadic macro support, |
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for the undocumented macro BOOST_PP_IS_EMPTY in the Boost |
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PP library. The code is taken from a posting by Paul Mensonides |
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of a variadic version for BOOST_PP_IS_EMPTY, and changed |
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in order to also support VC++. The code for the C++20 |
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implementation of the macro, using the __VA_OPT__ preprocessor |
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construct, is the author's own and reuses code added to the |
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Boost preprocessor library by this author. |
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... = variadic input, for VC++8 this must be a single parameter |
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returns = 1 if the input is empty, 0 if it is not |
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It is recommended to append BOOST_PP_EMPTY() to whatever input |
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is being tested in order to avoid possible warning messages |
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from some compilers about no parameters being passed to the macro |
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when the input is truly empty. |
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*/ |
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#if BOOST_VMD_MSVC_V8 |
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#define BOOST_VMD_IS_EMPTY(sequence) \ |
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BOOST_VMD_DETAIL_IS_EMPTY_IIF \ |
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( \ |
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BOOST_PP_IS_BEGIN_PARENS \ |
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( \ |
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sequence \ |
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) \ |
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) \ |
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( \ |
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BOOST_VMD_DETAIL_IS_EMPTY_GEN_ZERO, \ |
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BOOST_VMD_DETAIL_IS_EMPTY_PROCESS \ |
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) \ |
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(sequence) \ |
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/**/ |
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#else |
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# if defined(__cplusplus) && __cplusplus > 201703L |
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#include <boost/preprocessor/variadic/has_opt.hpp> |
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#include <boost/preprocessor/facilities/is_empty.hpp> |
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#define BOOST_VMD_IS_EMPTY(...) \ |
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BOOST_VMD_DETAIL_IS_EMPTY_IIF \ |
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( \ |
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BOOST_PP_VARIADIC_HAS_OPT() \ |
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) \ |
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( \ |
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BOOST_PP_IS_EMPTY_OPT, \ |
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BOOST_VMD_IS_EMPTY_NO_OPT \ |
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) \ |
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(__VA_ARGS__) \ |
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/**/ |
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# else |
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#define BOOST_VMD_IS_EMPTY(...) \ |
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BOOST_VMD_IS_EMPTY_NO_OPT(__VA_ARGS__) \ |
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/**/ |
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# endif |
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#define BOOST_VMD_IS_EMPTY_NO_OPT(...) \ |
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BOOST_VMD_DETAIL_IS_EMPTY_IIF \ |
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( \ |
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BOOST_PP_IS_BEGIN_PARENS \ |
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( \ |
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__VA_ARGS__ \ |
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) \ |
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) \ |
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( \ |
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BOOST_VMD_DETAIL_IS_EMPTY_GEN_ZERO, \ |
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BOOST_VMD_DETAIL_IS_EMPTY_PROCESS \ |
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) \ |
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(__VA_ARGS__) \ |
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/**/ |
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#endif /* BOOST_VMD_MSVC_V8 */ |
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#endif /* BOOST_PP_VARIADICS */ |
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#endif /* BOOST_VMD_IS_EMPTY_HPP */
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