template<typename RetType>

ark::callback struct

a movable noncopyable unique_function invoked to signal completion

Template parameters
RetType	if void, the signature of callback function is void(), otherwise void(RetType ret)

arkio callbacks are function2::unique_function, which is just like std::function but movable and non-copyable. So, it is safe to move capture values, and use the async io operation to prolong their lifetime inside async_context.

ahout function2 : https://github.com/Naios/function2 the document for unique_function is inside readme

Public types

using ret_type = RetType