6_Objective-C Extensions

Extensions are actually categories without the category name. It’s often referred as anonymous categories.

The methods declared by a class extension are implemented in the implementation block for the original class, so you can’t, for example, declare a class extension on a framework class, such as a Cocoa or Cocoa Touch class like NSString..

Syntax
@interface ClassName ()
@end

Characteristics of extensions

  • An extension cannot be declared for any class, only for the classes that we have original implementation of source code.
  • An extension is adding private methods and private variables that are only specific to the class.
  • Any method or variable declared inside the extensions is not accessible even to the inherited classes.

Example of extension

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