71 lines
1.8 KiB
C++
71 lines
1.8 KiB
C++
/* Copyright 2017 Joaquin M Lopez Munoz.
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* Distributed under the Boost Software License, Version 1.0.
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* (See accompanying file LICENSE_1_0.txt or copy at
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* http://www.boost.org/LICENSE_1_0.txt)
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*
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* See http://www.boost.org/libs/poly_collection for library home page.
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*/
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#ifndef BOOST_POLY_COLLECTION_DETAIL_IS_LIKELY_STATELESS_LAMBDA_HPP
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#define BOOST_POLY_COLLECTION_DETAIL_IS_LIKELY_STATELESS_LAMBDA_HPP
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#if defined(_MSC_VER)
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#pragma once
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#endif
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#include <type_traits>
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namespace boost{
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namespace poly_collection{
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namespace detail{
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/* Stateless lambda expressions have one (and only one) call operator and are
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* convertible to a function pointer with the same signature. Non-lambda types
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* could satisfy this too, hence the "likely" qualifier.
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*/
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template<typename T>
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struct has_one_operator_call_helper
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{
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template<typename Q> static std::true_type test(decltype(&Q::operator())*);
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template<typename> static std::false_type test(...);
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using type=decltype(test<T>(nullptr));
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};
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template<typename T>
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using has_one_operator_call=typename has_one_operator_call_helper<T>::type;
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template<typename T>
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struct equivalent_function_pointer
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{
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template<typename Q,typename R,typename... Args>
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static auto helper(R (Q::*)(Args...)const)->R(*)(Args...);
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template<typename Q,typename R,typename... Args>
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static auto helper(R (Q::*)(Args...))->R(*)(Args...);
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using type=decltype(helper(&T::operator()));
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};
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template<typename T,typename=void>
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struct is_likely_stateless_lambda:std::false_type{};
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template<typename T>
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struct is_likely_stateless_lambda<
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T,
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typename std::enable_if<has_one_operator_call<T>::value>::type
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>:std::is_convertible<
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T,
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typename equivalent_function_pointer<T>::type
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>{};
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} /* namespace poly_collection::detail */
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} /* namespace poly_collection */
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} /* namespace boost */
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#endif
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