Quick Tip: Don’t Do This

I could not find out where a bug was coming from for the life of me today. Naturally it one of those “assignment instead of equality” bugs that seem to crop up when trying to code too quickly. The difference here was that I had implemented a subclass of NSObject that reimplemented the method +resolveInstanceMethod:. So, the code went like this:

+ ( BOOL )resolveInstanceMethod:( SEL )sel
{
    if ( sel = @selector( setFoobar: )) {
        return class_addMethod([ self class ], sel, ( IMP )setFB, "v@:@" );
    } else if ( sel = @selector( foobar )) {
        return class_addMethod([ self class ], sel, ( IMP )getFB, "@@:" );
    } else {
        return [ super resolveInstanceMethod:sel ];
    }
}

For those of you keeping score at home, when the Objective-C runtime tried to resolve any selector, this method happily added a selector for -setFoobar: to self’s class and returned YES.

Don’t do this.