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