How does class composition work in iOS?

Question

Let\'s say I have property A on classA and property B on classB and I want classAB to have both properties <

Answer 1

Assuming ClassA and ClassB are implemented as you said, this works very well, and is easily extendable.

@interface ClassAB : NSObject

@property int a;
@property int b;

@property ClassA *aObject;
@property ClassB *bObject;

@end

@implementation ClassAB

@dynamic a, b;
@synthesize aObject, bObject;

-(id) forwardingTargetForSelector:(SEL)aSelector
{
    if ([aObject respondsToSelector:aSelector])
        return aObject;
    else if ([bObject respondsToSelector:aSelector])
        return bObject;

    return nil;    
}

@end

int main(int argc, const char * argv[])
{
    @autoreleasepool {
        ClassA *a = [ClassA new];
        ClassB *b = [ClassB new];

        ClassAB *ab = [ClassAB new];
        ab.aObject = a;
        ab.bObject = b;

        ab.a = 10;
        ab.b = 20;

        NSLog(@"%i, %i", a.a, b.b); // outputs 10, 20
    }
    return 0;
}