wrapping.m

- (id)forwardingTargetForSelector:(SEL const)aSelector
{
    if(   aSelector == @selector(a)
       || aSelector == @selector(b)
       || aSelector == @selector(c))
        return _wrappedObject;
    else
        return nil;
}
- (void)setValue:(id const)aValue forUndefinedKey:(NSString * const)aKey
{
    @try {
        [_wrappedObject setValue:aValue forKey:aKey];
    } @catch(NSException *ignored) {
        [super setValue:aValue forUndefinedKey:aKey];
    }
}
- (id)valueForUndefinedKey:(NSString * const)aKey
{
    @try {
        return [_wrappedObject valueForKey:aKey];
    } @catch(NSException *ignored) {
        return [super valueForUndefinedKey:aKey];
    }
}