kvo-template.m

@interface Person : NSObject

@property (nonatomic, copy) NSMutableArray *friendNames;

@end

@implementation Person

- (id)init{
    self = [super init];
    if (self) {
        _friendNames = [[NSMutableArray alloc] init];
    }
    return self;
}

- (NSMutableArray *)friendNames {
    return [self mutableArrayValueForKey:@"friendNames"];
}

- (void)insertObject:(NSString *)object inFriendNamesAtIndex:(NSUInteger)index {
    [_friendNames insertObject:object atIndex:index];
}

- (void)removeObjectFromFriendNamesAtIndex:(NSUInteger)index {
    [_friendNames removeObjectAtIndex:index];
}

@end