iOS Singleton snippet

Singleton.h

@interface Singleton

+(Singleton*)sharedSingleton;

@end

Singleton.m

@implementation Singleton

static Singleton *_sharedSingleton;

+(Singleton*)sharedSingleton{
    @synchronized([Singleton class])
    {
        if(!_sharedSingleton)
            _sharedSingleton = [[self alloc] init];
        return _sharedSingleton;
    }
    return nil;
}

+(id)alloc
{
    @synchronized([Singleton class])
    {
        NSAssert(_sharedSingleton == nil, @"Attempted to allocate a second instance of the Singleton singleton");
        _sharedSingleton = [super alloc];
        return _sharedSingleton;
    }
    return nil;
}

@end