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Diffstat (limited to 'boost/poly_collection/detail/is_likely_stateless_lambda.hpp')
-rw-r--r-- | boost/poly_collection/detail/is_likely_stateless_lambda.hpp | 70 |
1 files changed, 70 insertions, 0 deletions
diff --git a/boost/poly_collection/detail/is_likely_stateless_lambda.hpp b/boost/poly_collection/detail/is_likely_stateless_lambda.hpp new file mode 100644 index 0000000000..d8469c0dd3 --- /dev/null +++ b/boost/poly_collection/detail/is_likely_stateless_lambda.hpp @@ -0,0 +1,70 @@ +/* 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_POLY_COLLECTION_DETAIL_IS_LIKELY_STATELESS_LAMBDA_HPP +#define BOOST_POLY_COLLECTION_DETAIL_IS_LIKELY_STATELESS_LAMBDA_HPP + +#if defined(_MSC_VER) +#pragma once +#endif + +#include <type_traits> + +namespace boost{ + +namespace poly_collection{ + +namespace 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 std::true_type test(decltype(&Q::operator())*); + template<typename> static std::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:std::false_type{}; + +template<typename T> +struct is_likely_stateless_lambda< + T, + typename std::enable_if<has_one_operator_call<T>::value>::type +>:std::is_convertible< + T, + typename equivalent_function_pointer<T>::type +>{}; + +} /* namespace poly_collection::detail */ + +} /* namespace poly_collection */ + +} /* namespace boost */ + +#endif |