/*============================================================================= Copyright (c) 2015 Paul Fultz II constexpr_deduce.h 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) ==============================================================================*/ #ifndef BOOST_HOF_GUARD_FUNCTION_CONSTEXPR_DEDUCE_H #define BOOST_HOF_GUARD_FUNCTION_CONSTEXPR_DEDUCE_H #include <boost/hof/config.hpp> #define BOOST_HOF_CONST_FOLD(x) (__builtin_constant_p(x) ? (x) : (x)) #ifndef BOOST_HOF_HAS_CONST_FOLD #if defined(__GNUC__) && !defined (__clang__) && __GNUC__ == 4 && __GNUC_MINOR__ < 7 #define BOOST_HOF_HAS_CONST_FOLD 0 #elif defined(__clang__) || defined (__GNUC__) #define BOOST_HOF_HAS_CONST_FOLD 1 #else #define BOOST_HOF_HAS_CONST_FOLD 0 #endif #endif namespace boost { namespace hof { namespace detail { struct constexpr_deduce { constexpr constexpr_deduce() {} template<class F> constexpr operator F() const { return F(); } }; template<class T> struct constexpr_deduce_unique { constexpr constexpr_deduce_unique() {} #if BOOST_HOF_HAS_CONST_FOLD template<class F> constexpr operator const F&() const { static_assert(BOOST_HOF_IS_EMPTY(F), "Function or lambda expression must be empty"); return BOOST_HOF_CONST_FOLD(reinterpret_cast<const F&>(static_const_var<T>())); } #else template<class F> constexpr operator F() const { // static_assert(std::is_default_constructible<F>::value, "Function not default constructible"); return F(); } #endif }; }}} // namespace boost::hof #define BOOST_HOF_DETAIL_CONSTEXPR_DEDUCE true ? boost::hof::detail::constexpr_deduce() : #define BOOST_HOF_DETAIL_CONSTEXPR_DEDUCE_UNIQUE(T) true ? boost::hof::detail::constexpr_deduce_unique<T>() : #ifdef _MSC_VER #define BOOST_HOF_DETAIL_MSVC_CONSTEXPR_DEDUCE BOOST_HOF_DETAIL_CONSTEXPR_DEDUCE #else #define BOOST_HOF_DETAIL_MSVC_CONSTEXPR_DEDUCE #endif #endif