Mac OS X Leopard - ARCAism

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CHAPTER 26 MAC OS X DEVELOPMENT: OBJECTIVE-C
@implementation NSString (BMString)
- (NSString *)stringByPrependingString:(NSString *)aString;
{
return [aString stringByAppendingString:self];
}
@end
Now prepending a string works as expected:
NSString *greeting = @", world!";
greeting = [greeting stringByPrependingString:@"Hello"];
NSLog(greeting);
Hello, world!
Unlike a subclass, we have access to everything in the NSString class, including private members.
Indeed, when you’re writing a category, the hardest thing to remember is that you’re inside
the class you’re categorizing. Try not to let the power go to your head, or the next section will
really blow your mind.
Method Swizzling
It’s one thing to add methods to a class, but the inheritance model offers something categories
don’t. Namely, a subclass can override a superclass’s implementation. That is, it doesn’t just add
behavior; it can change behavior. Objective-C lets you do this and more. Since method implementations
are data, you can swap any class’s implementation with your own, a trick called
swizzling.
For example, consider the description method, as implemented by NSXMLNode. It just spits out
raw XML, without any whitespace. I’ll show you what I mean. Consider the following snippet
of XML, a bit of syndicated web content created by iWeb:
My Blog
http://www.worldofkevin.com/Site/Blog/Blog.html
Welcome to my blog: Alit, Enit, Laore, Eros Vel, Exer Dolorer,
Niam Lut.
iWeb 1.1.2
http://www.worldofkevin.com/Site/Blog/Blog_files/200206373-3-a.png
My Blog
http://www.worldofkevin.com/Site/Blog/Blog.html
Red Vines: the perfect super food
http://www.worldofkevin.com/Site/Blog/88DD8356-E484-44DD-9419-
AE9F936E8BAD.html
http://www.worldofkevin.com/Site/Blog/88DD8356-E484-44DD-9419-
AE9F936E8BAD.html
Mon, 20 Aug 2007 10:48:11 -0700
<a href='http://www.worldofkevin.com/Site/Blog/
88DD8356-E484-44DD-9419-AE9F936E8BAD_files/FD004359-1.jpg'><img