ObjC_Singleton.m

@interface Singleton : NSObject
@end

@implementation Singleton

+ (instancetype)sharedInstance {
    static Singleton *sharedInstance = nil;
    static dispatch_once_t onceToken;

    dispatch_once(&onceToken, ^{
        sharedInstance = [[Singleton alloc] init];
    });
    return sharedInstance;
}

@end