This is a feature of the Objective-C compiler rather than of the runtime, anyway since it is documented nowhere and its existence was forgotten, we are documenting it here.
@compatibility_alias allows you to define a class name
as equivalent to another class name. For example:
@compatibility_alias WOApplication GSWApplication;
tells the compiler that each time it encounters
a class name, it should replace it with
GSWApplication (that is,
WOApplication is just an alias for
There are some constraints on how this can be used--
WOApplication(the alias) must not be an existing class;
GSWApplication(the real class) must be an existing class.