Mac OS X Leopard - ARCAism

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CHAPTER 26 MAC OS X DEVELOPMENT: OBJECTIVE-C
• Create derived properties. For example, you might later decide to derive name from
properties called firstName and lastName.
• Create dependent keys, such that a change to one key triggers change notifications in other
keys.
• Sync keys to other keys using bindings, the zero-code technology that gives Interface
Builder much of its power.
• Bridge properties between Objective-C and other technologies such as Core Data and
AppleScript.
Objective-C 2.0
Apple has long contributed to the usefulness of Objective-C. Apple has done this directly by contributing
to the GNU open source projects that compile, debug, and link Objective-C applications.
They’ve also done this indirectly by providing frameworks such as Cocoa. With Leopard, Apple
has finally begun to improve the language itself in an effort known as Objective-C 2.0.
Class Extension
One of the most common uses of Objective-C’s method categories is the creation of private
headers. These define methods that are used by the internal implementation of a class but should
not be called from outside the class.
In a way, this is an abuse of the language. Categories are meant to arrange a class’s implementation
by functionality. Using a category to define private methods creates an artificial
separation in the implementation based on visibility, rather than function.
Class extensions are a new kind of “anonymous” category. Unlike a standard category,
which extends both the interface and the implementation, a class extension extends only the
interface. The implementation remains with the main class. Thus, a public method and closely
related private methods can remain together.
For example, say you had a contrived class whose public interface declared like this:
@interface MyClass : NSObject
- (void)publicMethod;
@end
Within your implementation file (or private header), you would declare the following:
@interface MyClass ()
- (void)privateMethod;
- (void)privateHelper;
@end
Then your implementation would look something like this:
@implementation MyClass
- (void)publicMethod;
{
[self privateMethod];
// ...
}