/* 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_TT_DETAIL_IS_LIKELY_STATELESS_LAMBDA_HPP
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#define BOOST_TT_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 <boost/type_traits/detail/config.hpp>
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#include <boost/type_traits/integral_constant.hpp>
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#if defined(BOOST_TT_HAS_ACCURATE_BINARY_OPERATOR_DETECTION)
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//
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// We don't need or use this, just define a dummy class:
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//
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namespace boost{ namespace type_traits_detail{
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template<typename T>
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struct is_likely_stateless_lambda : public false_type {};
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}}
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#elif !defined(BOOST_NO_CXX11_LAMBDAS) && !defined(BOOST_NO_CXX11_DECLTYPE) && !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !BOOST_WORKAROUND(BOOST_MSVC, < 1900)\
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&& !(BOOST_WORKAROUND(BOOST_MSVC, == 1900) && defined(__CLR_VER))
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#include <boost/type_traits/is_convertible.hpp>
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#include <boost/type_traits/enable_if.hpp>
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namespace boost{
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namespace type_traits_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 boost::true_type test(decltype(&Q::operator())*);
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template<typename> static boost::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 : 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 boost::enable_if_<has_one_operator_call<T>::value>::type> :
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boost::is_convertible<T, typename equivalent_function_pointer<T>::type
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>{};
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} /* namespace type_traits_detail */
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} /* namespace boost */
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#else
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//
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// Can't implement this:
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//
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namespace boost {
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namespace type_traits_detail {
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template<typename T>
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struct is_likely_stateless_lambda : public boost::integral_constant<bool, false> {};
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}}
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#endif
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#endif
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