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### 8.6 `compatibility_alias`

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.