Why use [ClassName alloc] instead of [[self class] alloc]?

Question

I\'m reading through Mark Dalrymple\'s Learn Objective-C on the Mac (only at the chapter on Protocols, so still relatively newbish) and trying to figure something out:<

Answer 1

Generally, within a class method, you do use [[self alloc] init]. For example, the canonical way to write a convenience method for a class is:

+ (id)fooWithBar:(Bar *)aBar
{
    return [[[self alloc] initWithBar:aBar] autorelease];
}

(Note that in a class method, self refers to the class object.)

However, you would use [[Foo alloc] init] (that is, an explicit class name) if you actually want an instance of the Foo class (and not a subclass).