iOS block解决循环引用的两个宏

非原创代码，具体出处已无处查找

//解决block循环引用
#ifndef    weakify
#if __has_feature(objc_arc)

#define weakify( x ) \
_Pragma("clang diagnostic push") \
_Pragma("clang diagnostic ignored \"-Wshadow\"") \
autoreleasepool{} __weak __typeof__(x) __weak_##x##__ = x; \
_Pragma("clang diagnostic pop")

#else

#define weakify( x ) \
_Pragma("clang diagnostic push") \
_Pragma("clang diagnostic ignored \"-Wshadow\"") \
autoreleasepool{} __block __typeof__(x) __block_##x##__ = x; \
_Pragma("clang diagnostic pop")

#endif
#endif

#ifndef    strongify
#if __has_feature(objc_arc)

#define strongify( x ) \
_Pragma("clang diagnostic push") \
_Pragma("clang diagnostic ignored \"-Wshadow\"") \
try{} @finally{} __typeof__(x) x = __weak_##x##__; \
_Pragma("clang diagnostic pop")

#else

#define strongify( x ) \
_Pragma("clang diagnostic push") \
_Pragma("clang diagnostic ignored \"-Wshadow\"") \
try{} @finally{} __typeof__(x) x = __block_##x##__; \
_Pragma("clang diagnostic pop")

#endif
#endif