宏定义快速构建单例模式

“#define single_implementation(class) \
static class *_instance; \
\
+ (class *)share \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [[self alloc]init]; \
}); \
return _instance; \
} \
\
+(instancetype)allocWithZone:(struct _NSZone *)zone \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [super allocWithZone:zone]; \
}); \
return _instance; \
}