单例

普通的

static Model *model;

+(id)signalton{
if(!model){
  @synchronized(self){
  model = [[Model alloc]init];
    }
}
return model;
}

GCD单例

  +(AccountManager *)sharedManager{
      static AccountManager *sharedManagerInstance = nil;
      static dispatch_once_t predicate;
      dispatch_once(&predicate,^{
          sharedAccountManagerInstance = [[self alloc]init];
  });
  return sharedAccountManagerInstance;
  }

swift单例

  class TestObject{
     private static let testObject = TestObject()
     static var shareInstance: TestObject{
        return testObject
    } 
     private init(){
     }
}


class MyManager{

    static let shareInstance = MyManager()

    private init(){}

}