Wrap a function object in a packaged task.
template< typename Function> unspecified operator()( Function && f) const;
The package
function is used to adapt a function object as
a packaged task. When this adapter is passed as a completion token to an
asynchronous operation, the result of the function object is retuned via
a std::future.
std::future<std::size_t> fut = my_socket.async_read_some(buffer, use_future([](asio::error_code ec, std::size_t n) { return ec ? 0 : n; })); ... std::size_t n = fut.get();