Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

Asynchronously send a message.

template<
    typename... Args,
    typename CompletionToken = DEFAULT>
DEDUCED async_send(
    Args &&... args,
    CompletionToken && token);

void(boost::system::error_code)