75 lines
2.0 KiB
C++
75 lines
2.0 KiB
C++
/*=============================================================================
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Copyright (c) 2015 Paul Fultz II
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constexpr_deduce.h
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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==============================================================================*/
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#ifndef BOOST_HOF_GUARD_FUNCTION_CONSTEXPR_DEDUCE_H
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#define BOOST_HOF_GUARD_FUNCTION_CONSTEXPR_DEDUCE_H
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#include <boost/hof/config.hpp>
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#define BOOST_HOF_CONST_FOLD(x) (__builtin_constant_p(x) ? (x) : (x))
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#ifndef BOOST_HOF_HAS_CONST_FOLD
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#if defined(__GNUC__) && !defined (__clang__) && __GNUC__ == 4 && __GNUC_MINOR__ < 7
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#define BOOST_HOF_HAS_CONST_FOLD 0
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#elif defined(__clang__) || defined (__GNUC__)
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#define BOOST_HOF_HAS_CONST_FOLD 1
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#else
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#define BOOST_HOF_HAS_CONST_FOLD 0
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#endif
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#endif
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namespace boost { namespace hof {
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namespace detail {
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struct constexpr_deduce
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{
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constexpr constexpr_deduce()
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{}
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template<class F>
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constexpr operator F() const
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{
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return F();
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}
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};
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template<class T>
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struct constexpr_deduce_unique
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{
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constexpr constexpr_deduce_unique()
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{}
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#if BOOST_HOF_HAS_CONST_FOLD
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template<class F>
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constexpr operator const F&() const
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{
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static_assert(BOOST_HOF_IS_EMPTY(F), "Function or lambda expression must be empty");
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return BOOST_HOF_CONST_FOLD(reinterpret_cast<const F&>(static_const_var<T>()));
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}
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#else
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template<class F>
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constexpr operator F() const
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{
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// static_assert(std::is_default_constructible<F>::value, "Function not default constructible");
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return F();
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}
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#endif
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};
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}}} // namespace boost::hof
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#define BOOST_HOF_DETAIL_CONSTEXPR_DEDUCE true ? boost::hof::detail::constexpr_deduce() :
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#define BOOST_HOF_DETAIL_CONSTEXPR_DEDUCE_UNIQUE(T) true ? boost::hof::detail::constexpr_deduce_unique<T>() :
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#ifdef _MSC_VER
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#define BOOST_HOF_DETAIL_MSVC_CONSTEXPR_DEDUCE BOOST_HOF_DETAIL_CONSTEXPR_DEDUCE
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#else
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#define BOOST_HOF_DETAIL_MSVC_CONSTEXPR_DEDUCE
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#endif
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#endif
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