NSInvocation

As you might imagine, it is handy to be able to package up a message—including the selector, the receiver, and all arguments—as an object that can be invoked at your leisure. Such an object is an instance of NSInvocation.

One exceedingly convenient use for invocations is in message forwarding. When an object is sent a message that it does not understand, the message-sending system, before raising an exception, checks whether the object has implemented