...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
template< typename ReadHandler = default_completion_token_t<executor_type>> DEDUCED async_fill( ReadHandler && handler = default_completion_token_t< executor_type >());
void(boost::system::error_code, std::size_t)