はてなブックマーク

Categories are a great way to add functionality to existing classes in Objective-C without extending them. Say you want to add a method to MD5 hash a particular string. A Java way of doing this would be to create your own string class by subclassing NSString and add the hashMD5 method to it. With Objective-C, you don't have to subclass at all, you can simply write a category on NSString that decla