本文介绍了一种使用Objective-C实现单例模式的方法，包括ARC和MRC两种内存管理模式下的实现细节。通过dispatch_once确保线程安全地初始化单例实例。
#define SingleH(name) + (instancetype)share##name;
#if __has_feature(objc_arc)
//条件满足 ARC
#define SingleM(name) static id _instance;\
+ (instancetype)allocWithZone:(struct _NSZone *)zone\
{\
}\
\
+ (instancetype)share##name{\
}\
\
- (id)copyWithZone:(NSZone *)zone{\
}\
\
- (id)mutableCopyWithZone:(NSZone *)zone{\
}
#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{\
}\
\
- (NSUInteger)retainCount{\
}
#endif
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