/* Copyright 2016-2017 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_INVOCABLE_HPP
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#define BOOST_POLY_COLLECTION_DETAIL_IS_INVOCABLE_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 <functional>
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#include <type_traits>
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/* technique explained at
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* http://bannalia.blogspot.com/2016/09/compile-time-checking-existence-of.html
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*/
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namespace boost{
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namespace poly_collection{
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namespace detail{
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namespace is_invocable_fallback{
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template <typename F,typename... Args>
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struct is_invocable:
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std::is_constructible<
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std::function<void(Args...)>,
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std::reference_wrapper<typename std::remove_reference<F>::type>
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>
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{};
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template <typename R,typename F,typename... Args>
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struct is_invocable_r:
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std::is_constructible<
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std::function<R(Args...)>,
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std::reference_wrapper<typename std::remove_reference<F>::type>
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>
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{};
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struct hook{};
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}}}}
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namespace std{
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template<>
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struct is_void< ::boost::poly_collection::detail::is_invocable_fallback::hook>:
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std::false_type
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{
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template<typename F,typename... Args>
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static constexpr bool is_invocable_f()
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{
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using namespace ::boost::poly_collection::detail::is_invocable_fallback;
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return is_invocable<F,Args...>::value;
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}
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template<typename R,typename F,typename... Args>
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static constexpr bool is_invocable_r_f()
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{
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using namespace ::boost::poly_collection::detail::is_invocable_fallback;
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return is_invocable_r<R,F,Args...>::value;
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}
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};
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} /* namespace std */
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namespace boost{
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namespace poly_collection{
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namespace detail{
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template<typename F,typename... Args>
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struct is_invocable:std::integral_constant<
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bool,
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std::is_void<is_invocable_fallback::hook>::template
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is_invocable_f<F,Args...>()
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>{};
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template<typename R,typename F,typename... Args>
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struct is_invocable_r:std::integral_constant<
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bool,
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std::is_void<is_invocable_fallback::hook>::template
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is_invocable_r_f<R,F,Args...>()
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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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