How XCode knows about name of function at compile time?

Question

I have written simple code to practice selector in Objective C, which is working fine

NSMutableArray *array = [NSMutableArray arrayWithObjects:@"A",@"B", nil];
NSLog(@"Before adding %@",array);

SEL message = @selector(addObject:); //I will change this line

if([array respondsToSelector:message])
{
    [array performSelector:message withObject:@"C"];
}

NSLog(@"After adding %@",array);

But as soon as I change selector line to,

SEL message = @selector(addobject:);// Just changed name of selector

XCode starts giving warning :

Undeclared selector 'addobject:'

Now, question is how XCode knows at compile time about name of method is correct or not. Is there always list of selector generates internally for whatever object I am creating? In this case for NSMutableArray

Answer 1

All Xcode knows is that there is no class, either in the system code or in your program, that declares a selector called addobject. You can prove this by creating a custom class that declares an addobject method, and the warning should go away, but of course the program will crash with a unrecognized selector sent to object error message.