Objective C GCD singleton

singleton.m

+ (MyObject *)sharedInstance
{
    static MyObject *instance;
    static dispatch_once_t onceToken;

    if (instance==nil) {
        dispatch_once(&onceToken, ^{
            instance = [[MyObject alloc] init];
        });
    }
    return instance;
}

u can remove "if (instance==nil)", GCD launches block only once! no matter to check for nil.

this is valid GCD singleton code:

+ (id *) sharedObject
{
    static id * _sharedObject = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _sharedObject = [NSObject new];
    });
    return _sharedObject;
}