### 7.5 compatibility_alias

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.

The keyword `@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 `WOApplication` as a class name, it should replace it with `GSWApplication` (that is, `WOApplication` is just an alias for `GSWApplication`).

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.