简单单例模式的书写

‘# 简单的单例

oc:

+(instancetype)sharedInstance
 {
  static id sharedInstance = nil;

  static dispath_once_t onceToken;
  dispatch_once(&onceToken, ^{

  sharedInstance = [[self alloc]init];
  });

  return sharedInstance;

  }

swift:

static let sharedInstance : <#SingletonClass#> = <#SingletonClass#> ()