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< typename decay< CompletionToken >::type, typename decay< Values >::type...> prepend( CompletionToken && completion_token, Values &&... values);
Header: asio/experimental/prepend.hpp
Convenience header: None