Mac OS X Leopard - ARCAism

NOTE In Java, you can override ivars with arguments, because you can distinguish them with
the keyword this. So, you could say this.name == name. Objective-C doesn’t have this nicety
(or hassle, depending on your point of view).
In a way, setters are written backward. You’re setting the value of the pointer to a new
object, which you will retain:
name = [aName retain];
Doing so will remove your ability to reach the old object, so you must first release it:
[name release];
However, if the old object and the new object are the same, you might end up causing the
object to be freed, which would cause a crash when you tried to use it. As such, before you can
do any of this, you need to check that the two objects are, in fact, not the same, and bail out if
they are:
if (name == aName)
return;
With all the fuss, it seems like it would be a lot easier to just access the variables directly and
not hassle with calling methods. However, there’s a good reason not to; it’s a violation of
encapsulation.
Encapsulation is an important part of object-oriented programming. It states that implementation
details should always be hidden. This prevents objects from becoming entangled and
making things just as complicated as they were with procedural programming. It also protects
programmers from implementation changes.
For example, consider the setter for age:
- (void)setAge:(NSUInteger)anAge;
{
age = anAge;
}
Right now it’s very simple. It takes a scalar type rather than a pointer, so we don’t even have
to worry about memory management. What if you later decide that blithely setting this value is
a security risk because of integer overflow exploits? To protect against that, you add some validation
logic:
- (void)setAge:(NSUInteger)anAge;
{
if (anAge > 0 && anAge < 100)
age = anAge;
}
CHAPTER 26 MAC OS X DEVELOPMENT: OBJECTIVE-C 495
If you’ve been good and respected encapsulation, your work is done. If you’ve been bad and
have been setting the variable directly, you’re going to have a lot of implementation work ahead
of you. That’s why it’s always a good idea to use setters and getters, even from within the object
itself.
NOTE In the section on Objective-C 2.0, you’ll read about Leopard’s new property syntax,
which makes writing setters and getters yesterday’s hassle.