### use_future_t

A completion token type that causes an asynchronous operation to return a future.

    template<
        typename Allocator = std::allocator<void>>
    class use_future_t

##### Types

Name | Description
--- | ---
allocator_type | The allocator type. The allocator is used when constructing the std::promise object for a given asynchronous operation.

##### Member Functions

Name | Description
--- | ---
get_allocator | Obtain allocator.
operator() | Wrap a function object in a packaged task. —
rebind | Specify an alternate allocator.
use_future_t [constructor] | Construct using default-constructed allocator. — Construct using specified allocator.

The `use_future_t` class is a completion token type that is used to indicate that an asynchronous operation should return a std::future object. A `use_future_t` object may be passed as a completion token to an asynchronous operation, typically using the special value `asio::use_future`. For example:

    std::future<std::size_t> my_future
     = my_socket.async_read_some(my_buffer, asio::use_future);

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.

##### Requirements

Header: `asio/use_future.hpp`

Convenience header: `asio.hpp`