async_patterns::Callback< ReturnType(Args...)>

#include <callback.h>

An asynchronous |Callback| that will always execute on the async dispatcher associated with a |Receiver|.

Summary

Invoking this callback translates to posting a task to the destination dispatcher. It will not block the caller.

The receiver may not necessarily receive the callback. The callback will be a no-op if:

  • The |Receiver| object goes out of scope.
  • The async dispatcher of the |Receiver| shuts down.

A callback can only be invoked once. It is akin to a one-shot, uni-directional channel. Calls posted to the same |Receiver| will be processed in the order they are made, regardless which |Function|s and |Callback|s they are made from.

Friend classes
::async_patterns::Receiver
friend class

Public functions
ignore_result()&&
auto
Returns a functor that performs the same actions as this |Callback|, but returns void, instead of potentially a promise object.
operator()(Args... args)
auto
Schedules the callback to be asynchronously run on the receiver's dispatcher.

Friend classes

::async_patterns::Receiver

friend class ::async_patterns::Receiver

Public functions

ignore_result

auto ignore_result()&&

Returns a functor that performs the same actions as this |Callback|, but returns void, instead of potentially a promise object.

This is useful when converting the |Callback| into a |fit::callback

operator()

auto operator()(
  Args... args
)

Schedules the callback to be asynchronously run on the receiver's dispatcher.

See |async_patterns::BindForSending| for detailed requirements on |args|.

This operator returns a pending call. You may either:

  • Make a fire-and-forget call, by discarding the returned object, or
  • Get a promise carrying the return value of the function by calling promise() on the object, yielding a |fpromise::promise|, or
  • Call Then() on the object and pass a |Callback|

See |async_patterns::PendingCall| for details.

Example: 

async_patterns::Callback<int(std::string)> parse = ...;

// Ignore the returned integer.
parse(std::string("abc"));

// Get a promise that will resolve when the function is asynchronously
// executed on the receiver's async dispatcher.
fpromise::promise promise = parse(std::string("abc")).promise();