[代码片段] weakify 和 strongify

#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