thread-safe objective c singleton syntax

Singleton.m

//
// Created by craigrbruce on 1/03/13.
//
// To change the template use AppCode | Preferences | File Templates.
//


#import "Singleton.h"


@implementation Singleton {

}
-(id)init
{
    NSAssert(NO, @"Cannot instantiate a singleton");
    return nil;
}
-(id)initSingleton{

    self = [super init];
    if (self){
        //do stuff here.
    }

    return self;
}

- (void)doStuff {

}
+(Singleton *) sharedSingleton{

    static dispatch_once_t  pred;
    static Singleton* instance = nil;
    dispatch_once(&pred, ^{instance = [[self alloc]initSingleton];});
    return instance;
}

@end