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/*=============================================================================
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
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