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//
// use_future.hpp
// ~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2016 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 BOOST_ASIO_USE_FUTURE_HPP
#define BOOST_ASIO_USE_FUTURE_HPP
#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
#include <boost/asio/detail/config.hpp>
#include <memory>
#include <boost/asio/detail/push_options.hpp>
namespace boost {
namespace asio {
/// Class used to specify that an asynchronous operation should return a future.
/**
* The use_future_t class is used to indicate that an asynchronous operation
* should return a std::future object. A use_future_t object may be passed as a
* handler to an asynchronous operation, typically using the special value @c
* boost::asio::use_future. For example:
*
* @code std::future<std::size_t> my_future
* = my_socket.async_read_some(my_buffer, boost::asio::use_future); @endcode
*
* The initiating function (async_read_some in the above example) returns a
* future that will receive the result of the operation. If the operation
* completes with an error_code indicating failure, it is converted into a
* system_error and passed back to the caller via the future.
*/
template <typename Allocator = std::allocator<void> >
class use_future_t
{
public:
/// The allocator type. The allocator is used when constructing the
/// @c std::promise object for a given asynchronous operation.
typedef Allocator allocator_type;
/// Construct using default-constructed allocator.
BOOST_ASIO_CONSTEXPR use_future_t()
{
}
/// Construct using specified allocator.
explicit use_future_t(const Allocator& allocator)
: allocator_(allocator)
{
}
/// Specify an alternate allocator.
template <typename OtherAllocator>
use_future_t<OtherAllocator> operator[](const OtherAllocator& allocator) const
{
return use_future_t<OtherAllocator>(allocator);
}
/// Obtain allocator.
allocator_type get_allocator() const
{
return allocator_;
}
private:
Allocator allocator_;
};
/// A special value, similar to std::nothrow.
/**
* See the documentation for boost::asio::use_future_t for a usage example.
*/
#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
constexpr use_future_t<> use_future;
#elif defined(BOOST_ASIO_MSVC)
__declspec(selectany) use_future_t<> use_future;
#endif
} // namespace asio
} // namespace boost
#include <boost/asio/detail/pop_options.hpp>
#include <boost/asio/impl/use_future.hpp>
#endif // BOOST_ASIO_USE_FUTURE_HPP
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