Completion token type used to specify that the completion handler arguments should be passed additional values before the results of the operation.

template<
    typename CompletionToken,
    typename... Values>
constexpr prepend_t< decay_t< CompletionToken >, decay_t< Values >... > prepend(
    CompletionToken && completion_token,
    Values &&... values);

Requirements

Header: boost/asio/prepend.hpp

Convenience header: boost/asio.hpp