[iOS] Singleton pattern in objc, how to keep init private?

From https://stackoverflow.com/questions/7034971/singleton-pattern-in-objc-how-to-keep-init-private

Throw an exception in init

- (instancetype)init {
    [self doesNotRecognizeSelector:_cmd];
    return nil;
}

- (instancetype)initPrivate {
    self = [super init];
    if (self) {
    }
    return self;
}

+ (instancetype)sharedInstance {
    static MySingleton *sharedInstance;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedInstance = [[self alloc] initPrivate];
    });
    return sharedInstance;
}

Have init return your singleton

- (instancetype)init {
    return [[self class] sharedInstance];
}

- (instancetype)initPrivate {
    self = [super init];
    if (self) {
    }
    return self;
}

+ (instancetype)sharedInstance {
    static MySingleton2 *sharedInstance;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedInstance = [[self alloc] initPrivate];
    });
    return sharedInstance;
}