简化单例模式

HMSingleton.h（这个可以直接copy过去，拿到项目中去用）文件名
文件内容:
// .h文件
#define HMSingletonH(name) + (instancetype)shared##name;

// .m文件
#if __has_feature(objc_arc)

    #define HMSingletonM(name)     static id _instace;      + (id)allocWithZone:(struct _NSZone *)zone     {         static dispatch_once_t onceToken;         dispatch_once(&onceToken, ^{             _instace = [super allocWithZone:zone];         });         return _instace;     }      + (instancetype)shared##name     {         static dispatch_once_t onceToken;         dispatch_once(&onceToken, ^{             _instace = [[self alloc] init];         });         return _instace;     }      - (id)copyWithZone:(NSZone *)zone     {         return _instace;     }

#else

    #define HMSingletonM(name)     static id _instace;      + (id)allocWithZone:(struct _NSZone *)zone     {         static dispatch_once_t onceToken;         dispatch_once(&onceToken, ^{             _instace = [super allocWithZone:zone];         });         return _instace;     }      + (instancetype)shared##name     {         static dispatch_once_t onceToken;         dispatch_once(&onceToken, ^{             _instace = [[self alloc] init];         });         return _instace;     }      - (id)copyWithZone:(NSZone *)zone     {         return _instace;     }      - (oneway void)release { }     - (id)retain { return self; }     - (NSUInteger)retainCount { return 1;}     - (id)autorelease { return self;}

#endif