42 lines
1.4 KiB
Plaintext
42 lines
1.4 KiB
Plaintext
[/
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/ Copyright (c) 2003-2023 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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/
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/ Distributed under the Boost Software License, Version 1.0. (See accompanying
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/ file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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/]
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[section:futures Futures]
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The `boost::asio::use_future` completion token provides first-class support for
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returning a `std::future` from an asynchronous operation's initiating function.
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To use `boost::asio::use_future`, pass it to an asynchronous operation instead of
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a completion handler. For example:
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std::future<std::size_t> length =
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my_socket.async_read_some(my_buffer, boost::asio::use_future);
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Where a completion signature has the form:
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void handler(boost::system::error_code ec, result_type result);
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the initiating function returns a `std::future` templated on `result_type`.
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In the above example, this is `std::size_t`. If the asynchronous operation
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fails, the `error_code` is converted into a `system_error` exception and
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passed back to the caller through the future.
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Where a completion signature has the form:
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void handler(boost::system::error_code ec);
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the initiating function returns `std::future<void>`. As above, an error
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is passed back in the future as a `system_error` exception.
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[heading See Also]
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[link boost_asio.reference.use_future use_future],
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[link boost_asio.reference.use_future_t use_future_t],
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[link boost_asio.examples.cpp11_examples.futures Futures example (C++11)].
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[endsect]
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