iOS开发之单例宏抽取

// .h文件
#define SingletonH + (instancetype)sharedInstance;

// .m文件
#define SingletonM \
static id _instance; \
 \
+ (instancetype)allocWithZone:(struct _NSZone *)zone \
{ \
    static dispatch_once_t onceToken; \
    dispatch_once(&onceToken, ^{ \
        _instance = [super allocWithZone:zone]; \
    }); \
    return _instance; \
} \
 \
+ (instancetype)sharedInstance \
{ \
    static dispatch_once_t onceToken; \
    dispatch_once(&onceToken, ^{ \
        _instance = [[self alloc] init]; \
    }); \
    return _instance; \
} \
 \
- (id)copyWithZone:(NSZone *)zone \
{ \
    return _instance; \
}

在需要实现单例的类的.h和.m文件下分别写下这两个宏的实现，会自动实现shareInstance方法，返回该类的单例对象，省去了工程下的代码量.