Singleton

Singleton.m

#import <Foundation/Foundation.h>

@interface Singleton : NSObject
+ (instancetype)sharedManager;
@end

@implementation Singleton
+ (instancetype)sharedInstance {
   static Singleton *sharedInstance = nil;
   static dispatch_once_t onceToken;
   dispatch_once(&onceToken, ^{
      sharedInstance = [[self alloc] init];
   });
   return sharedInstance;
}
@end