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/* Copyright 2017 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/poly_collection for library home page.
*/
#ifndef BOOST_TT_DETAIL_IS_LIKELY_STATELESS_LAMBDA_HPP
#define BOOST_TT_DETAIL_IS_LIKELY_STATELESS_LAMBDA_HPP
#if defined(_MSC_VER)
#pragma once
#endif
#include <boost/type_traits/detail/config.hpp>
#include <boost/type_traits/integral_constant.hpp>
#if defined(BOOST_TT_HAS_ACCURATE_BINARY_OPERATOR_DETECTION)
//
// We don't need or use this, just define a dummy class:
//
namespace boost{ namespace type_traits_detail{
template<typename T>
struct is_likely_stateless_lambda : public false_type {};
}}
#elif !defined(BOOST_NO_CXX11_LAMBDAS) && !defined(BOOST_NO_CXX11_DECLTYPE) && !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !BOOST_WORKAROUND(BOOST_MSVC, < 1900)
#include <boost/type_traits/is_convertible.hpp>
#include <boost/core/enable_if.hpp>
namespace boost{
namespace type_traits_detail{
/* Stateless lambda expressions have one (and only one) call operator and are
* convertible to a function pointer with the same signature. Non-lambda types
* could satisfy this too, hence the "likely" qualifier.
*/
template<typename T>
struct has_one_operator_call_helper
{
template<typename Q> static boost::true_type test(decltype(&Q::operator())*);
template<typename> static boost::false_type test(...);
using type=decltype(test<T>(nullptr));
};
template<typename T>
using has_one_operator_call=typename has_one_operator_call_helper<T>::type;
template<typename T>
struct equivalent_function_pointer
{
template<typename Q,typename R,typename... Args>
static auto helper(R (Q::*)(Args...)const)->R(*)(Args...);
template<typename Q,typename R,typename... Args>
static auto helper(R (Q::*)(Args...))->R(*)(Args...);
using type=decltype(helper(&T::operator()));
};
template<typename T,typename=void>
struct is_likely_stateless_lambda : false_type{};
template<typename T>
struct is_likely_stateless_lambda<
T,
typename boost::enable_if_c<has_one_operator_call<T>::value>::type> :
boost::is_convertible<T, typename equivalent_function_pointer<T>::type
>{};
} /* namespace type_traits_detail */
} /* namespace boost */
#else
//
// Can't implement this:
//
namespace boost {
namespace type_traits_detail {
template<typename T>
struct is_likely_stateless_lambda : public boost::integral_constant<bool, false> {};
}}
#endif
#endif
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