Program 15-12 @selector question

[Wikiboo]

I've got stuck on:

Code: (Objective-C)

-(void) sort
{
[book sortUsingSelector: @selector(compareNames:)];
}

I don't really understand what selector is?

I've read chapter 9 again, but it's not very clear to me yet.
Can someone explain to me in some basic example what selector is and what function does it have?
And what does it do in Program 15-12?

[skochan]

In order to pass a reference to a method (compareNames:) as an argument to another method (sortUsingSelector:) you need to convert the method name into what's called a "signature" (it's type is SEL).  The @selector directive does this conversion for you. 

Hope this helps.

Cheers,

Steve