Question

In my class Deck i have

static Deck *gInstance = NULL;


+(Deck *) instance {
    @synchronized(self) {
        if (gInstance == NULL)
            gInstance = [[self alloc] init];
    }

    return (gInstance);
}

and an init method that looks like

-(id) init {

    if (gInstance != NULL) {
        return self;
    }

    self = [super init];

    if (self) {
       // Lots of clever things
    }
    gInstance = self;
    return self;

}

My concern here is mainly whether init is implemented correctly. Please let me know if what i wrote looks right to you.

Or … is there a way i can make init private and prevent people (myself included) from seeing it altogether?

Answer 1

That is a kind of odd singleton implementation. My favorite implementation is to use some newer functionality present in GCD.

+ (MyObj*)sharedObject;
{
    static dispatch_once_t once;
    static MyObj *sharedObj;
    dispatch_once(&once, ^ { shared = [[MyObj alloc] init]; });
    return shared;
}

I would recommend only doing that, nothing more, nothing less. Enforcing a strict singleton will only end in pain and is generally pointless and an anti-pattern.

As far as if there is anything strictly ‘wrong’ with your implementation, I believe you’d want to return gInstance in the initializer when it isn’t NULL, not self.