Singleton Class in Objective-C

SingletonClass.m

#import <Foundation/Foundation.h>

@interface SingletonClass : NSObject
@property (class, readonly) id sharedSingletonClass;
@end

@implementation SingletonClass

static SingletonClass *_sharedSingletonClass;

- (void)singletonInit {
    // do initialisation here
}

+ (instancetype)allocWithZone:(struct _NSZone *)zone {
    return [SingletonClass sharedSingletonClass];
}

+ (instancetype)sharedSingletonClass {
    static dispatch_once_t onceToken;

    dispatch_once(&onceToken,
                  ^{
                      _sharedSingletonClass = [[super allocWithZone:nil] init];

                      if(_sharedSingletonClass)
                          [_sharedSingletonClass singletonInit];
                  });

    return _sharedSingletonClass;
}

@end