Question

I have a situation where my subclass is not seeing the superclass’ instance variable x. The ivar is obviously @protected by default, so why do I get a compiler error “x undeclared”?

- (CGSize)hitSize
{
    // Compiler error
    return size;
}

EDIT: hitSize is a property of a protocol my subclass is conforming to. The problem was that I had hitSize @synthesized, which was the culprit. The question then is why can’t the synthesized getter see the ivar?

EDIT: Now that I found out the problem, I edited the question to ask why this is an error.

Answer 1

Joanna’s answers are both correct (though ivar synthesis doesn’t kick in on 32 bit Mac OS X).

The reason, though, is because allowing a subclass to synthesize access to a superclass’s internal state would quite explicitly break encapsulation. The decision was made to explicitly not allow that particular pattern in all cases, even within a single framework.

If a superclass provides storage for something, it should provide the access control and encapsulate the management of said memory. If a subclass needs to customize access, do so with care by overriding the getter/setter [and, preferably, calling the super to actually get/set the value].