iOS-简化单例模式（定义成宏 以后通用）

// .h文件
#define HMSingletonH + (instancetype)sharedInstance;

// .m文件
#define HMSingletonM static id _instance;  + (id)allocWithZone:(struct _NSZone *)zone {     static dispatch_once_t onceToken;     dispatch_once(&onceToken, ^{         _instance = [super allocWithZone:zone];     });     return _instance; }  + (instancetype)sharedInstance {     static dispatch_once_t onceToken;     dispatch_once(&onceToken, ^{         _instance = [[self alloc] init];     });     return _instance; }  - (id)copyWithZone:(NSZone *)zone {     return _instance; }