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//
// uses_executor.hpp
// ~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2018 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// 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)
//
#ifndef ASIO_USES_EXECUTOR_HPP
#define ASIO_USES_EXECUTOR_HPP
#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
#include "asio/detail/config.hpp"
#include "asio/detail/type_traits.hpp"
#include "asio/detail/push_options.hpp"
namespace asio {
/// A special type, similar to std::nothrow_t, used to disambiguate
/// constructors that accept executor arguments.
/**
* The executor_arg_t struct is an empty structure type used as a unique type
* to disambiguate constructor and function overloading. Specifically, some
* types have constructors with executor_arg_t as the first argument,
* immediately followed by an argument of a type that satisfies the Executor
* type requirements.
*/
struct executor_arg_t
{
/// Constructor.
ASIO_CONSTEXPR executor_arg_t() ASIO_NOEXCEPT
{
}
};
/// A special value, similar to std::nothrow, used to disambiguate constructors
/// that accept executor arguments.
/**
* See asio::executor_arg_t and asio::uses_executor
* for more information.
*/
#if defined(ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
constexpr executor_arg_t executor_arg;
#elif defined(ASIO_MSVC)
__declspec(selectany) executor_arg_t executor_arg;
#endif
/// The uses_executor trait detects whether a type T has an associated executor
/// that is convertible from type Executor.
/**
* Meets the BinaryTypeTrait requirements. The Asio library provides a
* definition that is derived from false_type. A program may specialize this
* template to derive from true_type for a user-defined type T that can be
* constructed with an executor, where the first argument of a constructor has
* type executor_arg_t and the second argument is convertible from type
* Executor.
*/
template <typename T, typename Executor>
struct uses_executor : false_type {};
} // namespace asio
#include "asio/detail/pop_options.hpp"
#endif // ASIO_USES_EXECUTOR_HPP
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