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//
// associated_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_ASSOCIATED_EXECUTOR_HPP
#define ASIO_ASSOCIATED_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/is_executor.hpp"
#include "asio/system_executor.hpp"
#include "asio/detail/push_options.hpp"
namespace asio {
namespace detail {
template <typename>
struct associated_executor_check
{
typedef void type;
};
template <typename T, typename E, typename = void>
struct associated_executor_impl
{
typedef E type;
static type get(const T&, const E& e) ASIO_NOEXCEPT
{
return e;
}
};
template <typename T, typename E>
struct associated_executor_impl<T, E,
typename associated_executor_check<typename T::executor_type>::type>
{
typedef typename T::executor_type type;
static type get(const T& t, const E&) ASIO_NOEXCEPT
{
return t.get_executor();
}
};
} // namespace detail
/// Traits type used to obtain the executor associated with an object.
/**
* A program may specialise this traits type if the @c T template parameter in
* the specialisation is a user-defined type. The template parameter @c
* Executor shall be a type meeting the Executor requirements.
*
* Specialisations shall meet the following requirements, where @c t is a const
* reference to an object of type @c T, and @c e is an object of type @c
* Executor.
*
* @li Provide a nested typedef @c type that identifies a type meeting the
* Executor requirements.
*
* @li Provide a noexcept static member function named @c get, callable as @c
* get(t) and with return type @c type.
*
* @li Provide a noexcept static member function named @c get, callable as @c
* get(t,e) and with return type @c type.
*/
template <typename T, typename Executor = system_executor>
struct associated_executor
{
/// If @c T has a nested type @c executor_type, <tt>T::executor_type</tt>.
/// Otherwise @c Executor.
#if defined(GENERATING_DOCUMENTATION)
typedef see_below type;
#else // defined(GENERATING_DOCUMENTATION)
typedef typename detail::associated_executor_impl<T, Executor>::type type;
#endif // defined(GENERATING_DOCUMENTATION)
/// If @c T has a nested type @c executor_type, returns
/// <tt>t.get_executor()</tt>. Otherwise returns @c ex.
static type get(const T& t,
const Executor& ex = Executor()) ASIO_NOEXCEPT
{
return detail::associated_executor_impl<T, Executor>::get(t, ex);
}
};
/// Helper function to obtain an object's associated executor.
/**
* @returns <tt>associated_executor<T>::get(t)</tt>
*/
template <typename T>
inline typename associated_executor<T>::type
get_associated_executor(const T& t) ASIO_NOEXCEPT
{
return associated_executor<T>::get(t);
}
/// Helper function to obtain an object's associated executor.
/**
* @returns <tt>associated_executor<T, Executor>::get(t, ex)</tt>
*/
template <typename T, typename Executor>
inline typename associated_executor<T, Executor>::type
get_associated_executor(const T& t, const Executor& ex,
typename enable_if<is_executor<
Executor>::value>::type* = 0) ASIO_NOEXCEPT
{
return associated_executor<T, Executor>::get(t, ex);
}
/// Helper function to obtain an object's associated executor.
/**
* @returns <tt>associated_executor<T, typename
* ExecutionContext::executor_type>::get(t, ctx.get_executor())</tt>
*/
template <typename T, typename ExecutionContext>
inline typename associated_executor<T,
typename ExecutionContext::executor_type>::type
get_associated_executor(const T& t, ExecutionContext& ctx,
typename enable_if<is_convertible<ExecutionContext&,
execution_context&>::value>::type* = 0) ASIO_NOEXCEPT
{
return associated_executor<T,
typename ExecutionContext::executor_type>::get(t, ctx.get_executor());
}
#if defined(ASIO_HAS_ALIAS_TEMPLATES)
template <typename T, typename Executor = system_executor>
using associated_executor_t = typename associated_executor<T, Executor>::type;
#endif // defined(ASIO_HAS_ALIAS_TEMPLATES)
} // namespace asio
#include "asio/detail/pop_options.hpp"
#endif // ASIO_ASSOCIATED_EXECUTOR_HPP
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