一句话实现单例模式

// .h文件的实现
#define SingletonH(methodName) + (instancetype)shared##methodName;

// .m文件的实现
#if __has_feature(objc_arc) // 是ARC
#define SingletonM(methodName) static id _instace = nil; + (id)allocWithZone:(struct _NSZone *)zone { if (_instace == nil) { static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ _instace = [super allocWithZone:zone]; }); } return _instace; } - (id)init { static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ _instace = [super init]; }); return _instace; } + (instancetype)shared##methodName { return [[self alloc] init]; } + (id)copyWithZone:(struct _NSZone *)zone { return _instace; } + (id)mutableCopyWithZone:(struct _NSZone *)zone { return _instace; }

#else // 不是ARC

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

#endif