用法：
weakify(self)
strongify(self)
定义：
#ifndef weakify
#if DEBUG
#if __has_feature(objc_arc)
#define weakify(object) __weak __typeof__(object) weak##_##object = object;
#else
#define weakify(object) __block __typeof__(object) block##_##object = object;
#endif
#else
#if __has_feature(objc_arc)
#define weakify(object) try{} @finally{} {} __weak __typeof__(object) weak##_##object = object;
#else
#define weakify(object) try{} @finally{} {} __block __typeof__(object) block##_##object = object;
#endif
#endif
#endif
#ifndef strongify
#if DEBUG
#if __has_feature(objc_arc)
#define strongify(object) __typeof__(object) object = weak##_##object;
#else
#define strongify(object) __typeof__(object) object = block##_##object;
#endif
#else
#if __has_feature(objc_arc)
#define strongify(object) try{} @finally{} __typeof__(object) object = weak##_##object;
#else
#define strongify(object) try{} @finally{} __typeof__(object) object = block##_##object;
#endif
#endif
#endif
