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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)\
- && !(BOOST_WORKAROUND(BOOST_MSVC, == 1900) && defined(__CLR_VER))
- #include <boost/type_traits/is_convertible.hpp>
- #include <boost/type_traits/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_<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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