單例

static Class *manager;

+ (instancetype)allocWithZone:(struct _NSZone *)zone {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        if (manager == nil) {
            manager = [super allocWithZone:zone];
        }
    });
    return manager;
}
+ (instancetype)manager {
    return [[self alloc]init];
}
- (instancetype)copyWithZone:(NSZone *)zone {
    return manager;
}
- (instancetype)mutableCopyWithZone:(NSZone *)zone {
    return manager;
}

單例宏

#define SingleH(name) +(instancetype)share##name;

#if __has_feature(objc_arc)
//條件滿足 ARC
#define SingleM(name) static id _instance;\
+(instancetype)allocWithZone:(struct _NSZone *)zone\
{\
static dispatch_once_t onceToken;\
dispatch_once(&onceToken, ^{\
_instance = [super allocWithZone:zone];\
});\
\
return _instance;\
}\
\
+(instancetype)share##name\
{\
return [[self alloc]init];\
}\
\
-(id)copyWithZone:(NSZone *)zone\
{\
return _instance;\
}\
\
-(id)mutableCopyWithZone:(NSZone *)zone\
{\
return _instance;\
}

#else
//MRC
#define SingleM(name) static id _instance;\
+(instancetype)allocWithZone:(struct _NSZone *)zone\
{\
static dispatch_once_t onceToken;\
dispatch_once(&onceToken, ^{\
_instance = [super allocWithZone:zone];\
});\
\
return _instance;\
}\
\
+(instancetype)share##name\
{\
return [[self alloc]init];\
}\
\
-(id)copyWithZone:(NSZone *)zone\
{\
return _instance;\
}\
\
-(id)mutableCopyWithZone:(NSZone *)zone\
{\
return _instance;\
}\
-(oneway void)release\
{\
}\
\
-(instancetype)retain\
{\
    return _instance;\
}\
\
-(NSUInteger)retainCount\
{\
    return MAXFLOAT;\
}
#endif