Singleton (ARC)

gistfile1.m

static ClassName* shared = nil;
 
+ (ClassName *)sharedInstance
{
    if(!shared)
    {
        static dispatch_once_t pred;    // Lock
        dispatch_once(&pred, ^{         // This code is called at most once per app
            shared = [[ClassName alloc] init];
        });
    }
    return shared;
}
 
- (void) dealloc
{
}