单例宏

//单例宏（懒汉式）的抽取,##可以拼接单个字符串,/可以拼接多个字符串

//.h文件的抽取

#define SHARED_INTERFACE(className) +(instancetype)shared##className;

//.m文件的抽取

#if !__has_feature(objc_arc)

#define SHARED_IMPLEMENTATION(className)\

static id instace;\

+(instancetype)allocWithZone:(struct _NSZone *)zone{\

     static dispatch_once_t onceToken;\

    dispatch_once(&onceToken, ^{\

        instace=[super allocWithZone:zone];\

    });\

    return instace;\

}\

+(instancetype)shared##className{\

    static dispatch_once_t onceToken;\

    dispatch_once(&onceToken, ^{\

        instace=[[self alloc]init];\

    });\

    return instace;\

}\

-(id)copyWithZone:(NSZone *)zone{\

    return instace;\

}\

-(NSUInteger)retainCount{\

    return ULONG_MAX;\

}\

-(instancetype)retain{\

    return instace;\

}\

-(oneway void)release{\

}\

-(instancetype)autorelease{\

    return instace;\

}

//ARC

#else

#define SHARED_IMPLEMENTATION(className)\

static id instace;\

+(instancetype)allocWithZone:(struct _NSZone *)zone{\

static dispatch_once_t onceToken;\

dispatch_once(&onceToken, ^{\

instace=[super allocWithZone:zone];\

});\

return instace;\

}\

+(instancetype)shared##className{\

static dispatch_once_t onceToken;\

dispatch_once(&onceToken, ^{\

instace=[[self alloc]init];\

});\

return instace;\

}\

-(id)copyWithZone:(NSZone *)zone{\

return instace;\

}

#endif