Question

can anyone tell me please why returnSet is returning as nil when there are lowercase characters in ‘program’

I have stepped through and the NSLog is definitely picking the variables out but when it addObject: it just doesn’t?

+ (NSSet *)variablesUsedInProgram:(id)program
{
    NSMutableSet *returnSet = [[NSMutableSet alloc]init];

    if ([program isKindOfClass:[NSArray class]]) {
        [program enumerateObjectsUsingBlock: ^(id obj, NSUInteger idx, BOOL *stop)
        {
            if ([obj isKindOfClass:[NSString class]]) {
                if ([obj rangeOfCharacterFromSet:[NSCharacterSet lowercaseLetterCharacterSet]].location != NSNotFound) {
                    NSLog(@"Variable: %@", obj);
                    [returnSet addObject:obj]; 
                }
            }
        }];
    }

    return returnSet;
}

Answer 1

The posted code has no bug. It cannot return a value of nil.

Your error is elsewhere.