### async_write

Start an asynchronous operation to write a certain amount of data to a stream.

    template<
        typename AsyncWriteStream,
        typename ConstBufferSequence,
        typename WriteHandler>
    void async_write(
        AsyncWriteStream & s,
        const ConstBufferSequence & buffers,
        WriteHandler handler);

    template<
        typename AsyncWriteStream,
        typename ConstBufferSequence,
        typename CompletionCondition,
        typename WriteHandler>
    void async_write(
        AsyncWriteStream & s,
        const ConstBufferSequence & buffers,
        CompletionCondition completion_condition,
        WriteHandler handler);

    template<
        typename AsyncWriteStream,
        typename Allocator,
        typename WriteHandler>
    void async_write(
        AsyncWriteStream & s,
        basic_streambuf< Allocator > & b,
        WriteHandler handler);

    template<
        typename AsyncWriteStream,
        typename Allocator,
        typename CompletionCondition,
        typename WriteHandler>
    void async_write(
        AsyncWriteStream & s,
        basic_streambuf< Allocator > & b,
        CompletionCondition completion_condition,
        WriteHandler handler);