how to block a superclass method to be called to a subclass

Question

I'm extending the functionality of a class with a subclass, and I'm doing some dirty stuff that make superclass methods dangerous (app will hang in a loop) in the context of the subclass. I know it's not a genius idea, but I'm going for the low-hanging fruit, right now it's gonna save me some time. Oh it's a dirty job, but someone's gotta do it.

Bottom line, I need to either block that method from outside, or throw an exception when it's called directly to the superclass. (But I still use it from the subclass, except with care).

What would be the best way to do this?

UPDATE ---

So this is what I went for. I'm not self-answering, as Boaz' answer mentions multiple valid ways to do this, this is just the way that suited me. In the subclass, I overrode the method like this:

- (int)dangerousMethod
{
  [NSException raise:@"Danger!" format:@"Do not call send this method directly to this subclass"];
  return nil;
}

I'm marking this as answered, but evidently that doesn't mean it's closed, further suggestions are welcome.

Answer 1

If you create the methods in your superclass as "private" then the subclass has no possible way of calling them. I'm not familiar with Objective C, but every other object oriented language I've seen has the "private" qualifier.

Answer 2

Just re-implement the unsafe method in your subclass and have it do nothing or throw an exception or re-implement it as safe, just as long as the new implementation doesn't call the unsafe superclass method.

For the C++ crew in here: Objective C doesn't let you mark methods as private. You can use its category system to split up the interface into separate files (thus hiding 'private' ones), but all methods on a class are public.

Answer 3

hi Steph,

note: I'm ObjC/Cocoa newcomer:

@implementation MyClass
-(void)myMethod:(NSString *)txt{
    if([self class] != [MyClass class]) return;
    NSLog(@"Hello");
}
@end

Peter

Answer 4

This article explains how to create private variables in Objective C. They aren't truly private, but from what I read, the compiler will throw a warning if you try to call them from the subclass.