Chris@16: //
Chris@16: // use_future.hpp
Chris@16: // ~~~~~~~~~~~~~~
Chris@16: //
Chris@101: // Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
Chris@16: //
Chris@16: // Distributed under the Boost Software License, Version 1.0. (See accompanying
Chris@16: // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
Chris@16: //
Chris@16: 
Chris@16: #ifndef BOOST_ASIO_USE_FUTURE_HPP
Chris@16: #define BOOST_ASIO_USE_FUTURE_HPP
Chris@16: 
Chris@16: #if defined(_MSC_VER) && (_MSC_VER >= 1200)
Chris@16: # pragma once
Chris@16: #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
Chris@16: 
Chris@16: #include <boost/asio/detail/config.hpp>
Chris@16: #include <memory>
Chris@16: 
Chris@16: #include <boost/asio/detail/push_options.hpp>
Chris@16: 
Chris@16: namespace boost {
Chris@16: namespace asio {
Chris@16: 
Chris@16: /// Class used to specify that an asynchronous operation should return a future.
Chris@16: /**
Chris@16:  * The use_future_t class is used to indicate that an asynchronous operation
Chris@16:  * should return a std::future object. A use_future_t object may be passed as a
Chris@16:  * handler to an asynchronous operation, typically using the special value @c
Chris@16:  * boost::asio::use_future. For example:
Chris@16:  *
Chris@16:  * @code std::future<std::size_t> my_future
Chris@16:  *   = my_socket.async_read_some(my_buffer, boost::asio::use_future); @endcode
Chris@16:  *
Chris@16:  * The initiating function (async_read_some in the above example) returns a
Chris@16:  * future that will receive the result of the operation. If the operation
Chris@16:  * completes with an error_code indicating failure, it is converted into a
Chris@16:  * system_error and passed back to the caller via the future.
Chris@16:  */
Chris@16: template <typename Allocator = std::allocator<void> >
Chris@16: class use_future_t
Chris@16: {
Chris@16: public:
Chris@16:   /// The allocator type. The allocator is used when constructing the
Chris@16:   /// @c std::promise object for a given asynchronous operation.
Chris@16:   typedef Allocator allocator_type;
Chris@16: 
Chris@16:   /// Construct using default-constructed allocator.
Chris@16:   BOOST_ASIO_CONSTEXPR use_future_t()
Chris@16:   {
Chris@16:   }
Chris@16: 
Chris@16:   /// Construct using specified allocator.
Chris@16:   explicit use_future_t(const Allocator& allocator)
Chris@16:     : allocator_(allocator)
Chris@16:   {
Chris@16:   }
Chris@16: 
Chris@16:   /// Specify an alternate allocator.
Chris@16:   template <typename OtherAllocator>
Chris@16:   use_future_t<OtherAllocator> operator[](const OtherAllocator& allocator) const
Chris@16:   {
Chris@16:     return use_future_t<OtherAllocator>(allocator);
Chris@16:   }
Chris@16: 
Chris@16:   /// Obtain allocator.
Chris@16:   allocator_type get_allocator() const
Chris@16:   {
Chris@16:     return allocator_;
Chris@16:   }
Chris@16: 
Chris@16: private:
Chris@16:   Allocator allocator_;
Chris@16: };
Chris@16: 
Chris@16: /// A special value, similar to std::nothrow.
Chris@16: /**
Chris@16:  * See the documentation for boost::asio::use_future_t for a usage example.
Chris@16:  */
Chris@16: #if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
Chris@16: constexpr use_future_t<> use_future;
Chris@16: #elif defined(BOOST_ASIO_MSVC)
Chris@16: __declspec(selectany) use_future_t<> use_future;
Chris@16: #endif
Chris@16: 
Chris@16: } // namespace asio
Chris@16: } // namespace boost
Chris@16: 
Chris@16: #include <boost/asio/detail/pop_options.hpp>
Chris@16: 
Chris@16: #include <boost/asio/impl/use_future.hpp>
Chris@16: 
Chris@16: #endif // BOOST_ASIO_USE_FUTURE_HPP