Mac OS X Leopard - ARCAism

+ (BMPerson *)personWithName:(NSString *)aName age:(NSUInteger)anAge;
That makes starting an implementation as easy as copying and pasting. Technically, method
declarations in the implementation section don’t require semicolons, but the compiler conveniently
ignores them.
The factory method has a simple implementation. You allocate a new person, set its name
and age, and return it. The body of a method begins and ends with curly braces:
{
}
BMPerson *newPerson = [[self alloc] init];
[newPerson setName:aName];
[newPerson setAge:anAge];
return [newPerson autorelease];
This is just a convenient shortcut for doing the same thing in code, but there are a few subtle
differences that are worth noting.
If you actually instantiated a BMPerson externally, you would do so by sending alloc to the
class:
BMPerson *newPerson = [[BMPerson alloc] init];
CHAPTER 26 MAC OS X DEVELOPMENT: OBJECTIVE-C 491
From within the class method, however, you send the message to self.
Behind the scenes, every method in Objective-C is converted into a function. When you send
a message to an object, the messaging system looks up the appropriate function and calls it.
Along with the arguments you provided in the message, a few more arguments are slipped in.
The first “secret” argument is a pointer to the object on which the function is being called. That
argument’s name is self.
As such, whenever an object needs to refer to itself, such as to call one of its own methods,
it simply sends a message to self. In an instance method, self refers to the instance, which is to
say, the object. Six different objects will get six different results by sending the same message
to self. In a class method, self refers to the class. Therefore, when a class calls its own class
method, such as alloc, it sends a message to itself, using self. It’s a fine point, but one to keep
in mind.
NOTE Objects also have a secret ivar called isa that refers to its class. Class methods can
therefore be called by sending a message to isa. However, runtime considerations make calling
isa a gamble, so it’s better to get your class indirectly, via [self class].
After setting the name and age that were passed in, you return the new object with the standard
C keyword return. Because you created it, you need to release it, but because you’re
returning it, you send it an autorelease message, as detailed in the previous section on memory
management.
To use this method in code, you send a message to the class:
BMPerson *worldsToughestProgrammer = [BMPerson personWithName:@"Mike Lee" age:31];
This is equivalent to creating an instance on your own, using almost the same code as you
used to implement the method.
BMPerson *worldsToughestProgrammer = [[BMPerson alloc] init];
[newPerson setName:@"Mike Lee"];
[newPerson setAge:31];