Previously we learn how to add methods from outside the class : Objective-C : Categories
Objective-C permits a class to wholly replace another class within a program. The replacing class is said to "pose as" the target class.
Note: Class posing was declared deprecated with Mac OS X v10.5, and is unavailable in the 64-bit runtime.
For the versions still supporting posing, all messages sent to the target class are instead received by the posing class.
There are several restrictions
• A class may only pose as one of its direct or indirect superclasses.
• The posing class must not define any new instance variables that are absent from the target class (though it may define or override methods).
• The target class may not have received any messages prior to the posing.
• Posing, similarly with categories, allows global augmentation of existing classes. Posing permits two features absent from categories:
• A posing class can call overridden methods through super, thus incorporating the implementation of the target class.
• A posing class can override methods defined in categories
@interface CustomNSApplication : NSApplication
- (void) setMainMenu: (NSMenu*) menu
// do something with menu
class_poseAs ([CustomNSApplication class], [NSApplication class]);
This intercepts every invocation of setMainMenu to NSApplication.