boost/flyweight/detail/not_placeholder_expr.hpp
/* Copyright 2006-2018 Joaquin M Lopez Munoz. * 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) * * See http://www.boost.org/libs/flyweight for library home page. */ #ifndef BOOST_FLYWEIGHT_DETAIL_NOT_PLACEHOLDER_EXPR_HPP #define BOOST_FLYWEIGHT_DETAIL_NOT_PLACEHOLDER_EXPR_HPP #if defined(_MSC_VER) #pragma once #endif /* BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION can be inserted at the end * of a class template parameter declaration: * template< * typename X0,...,typename Xn * BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION * > * struct foo... * to prevent instantiations from being treated as MPL placeholder * expressions in the presence of placeholder arguments; this is useful * to avoid masking of a metafunction class nested ::apply during * MPL invocation. */ #include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */ #include <boost/detail/workaround.hpp> #if BOOST_WORKAROUND(__GNUC__, <4)||\ BOOST_WORKAROUND(__GNUC__,==4)&&(__GNUC_MINOR__<2)||\ BOOST_WORKAROUND(__GNUC__, ==7)&&( __cplusplus>=201703L)||\ BOOST_WORKAROUND(__GNUC__, >=8)&&( __cplusplus>=201103L) /* The default trick on which the macro is based, namely adding a int=0 * defaulted template parameter, does not work in GCC prior to 4.2 due to * an unfortunate compiler non-standard extension, as explained in * http://lists.boost.org/boost-users/2007/07/29866.php * As it happens, GCC 7 in C++17 mode and GCC 8 (and presumably later) in * C++11 mode (and presumably later) go back to this old behavior, anticipating * the resolution of CWG DR 150 (see P0522R0). * In these cases we resort to an uglier technique, adding defaulted template * parameters so as to exceed BOOST_MPL_LIMIT_METAFUNCTION_ARITY. */ #include <boost/mpl/limits/arity.hpp> #include <boost/preprocessor/facilities/intercept.hpp> #include <boost/preprocessor/repetition/enum_trailing_params.hpp> #define BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION \ BOOST_PP_ENUM_TRAILING_PARAMS( \ BOOST_MPL_LIMIT_METAFUNCTION_ARITY,typename=int BOOST_PP_INTERCEPT) #define BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION_DEF \ BOOST_PP_ENUM_TRAILING_PARAMS( \ BOOST_MPL_LIMIT_METAFUNCTION_ARITY,typename BOOST_PP_INTERCEPT) #else #define BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION ,int=0 #define BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION_DEF ,int #endif #endif