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@strongify(self)解析

①通过

#define strongify(...) \try {} @finally {} \_Pragma("clang diagnostic push") \_Pragma("clang diagnostic ignored \"-Wshadow\"") \metamacro_foreach(rac_strongify_,, __VA_ARGS__) \_Pragma("clang diagnostic pop")

替换结果为：
@try {} @finally {}metamacro_foreach(rac_strongify_,, __VA_ARGS__)

②通过
#define metamacro_foreach(MACRO, SEP, ...) \metamacro_foreach_cxt(metamacro_foreach_iter, SEP, MACRO, __VA_ARGS__)

替换结果为：
@try {} @finally {}metamacro_foreach_cxt(metamacro_foreach_iter, , rac_strongify_, self)

③通过
#define metamacro_foreach_cxt(MACRO, SEP, CONTEXT, ...) \metamacro_concat(metamacro_foreach_cxt, metamacro_argcount(__VA_ARGS__))(MACRO, SEP, CONTEXT, __VA_ARGS__)

替换结果为：
@try {} @finally {}metamacro_concat(metamacro_foreach_cxt, metamacro_argcount(self))(metamacro_foreach_iter,, rac_strongify_, self)

【@strongify(self)解析】④通过
#define metamacro_argcount(...) \metamacro_at(20, __VA_ARGS__, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1) //返回当前参数的个数

替换结果为：
@try {} @finally {}metamacro_concat(metamacro_foreach_cxt, 1)(metamacro_foreach_iter,, rac_strongify_, self)

⑤通过
#define metamacro_concat_(A, B) A ## B

替换结果为：
@try {} @finally {}metamacro_foreach_cxt1(metamacro_foreach_iter,, rac_strongify_, self)

⑥通过
#define metamacro_foreach_cxt1(MACRO, SEP, CONTEXT, _0) MACRO(0, CONTEXT, _0)

替换结果为：
@try {} @finally {}metamacro_foreach_iter(0,rac_strongify_, self)

⑦通过
#define metamacro_foreach_iter(INDEX, MACRO, ARG) MACRO(INDEX, ARG)

替换结果为：
@try {} @finally {}rac_strongify_(0,self)

⑧通过
#define rac_strongify_(INDEX, VAR) \__strong __typeof__(VAR) VAR = metamacro_concat(VAR, _weak_);

替换结果为：
@try {} @finally {}__strong __typeof__(self) self = self_weak_;

注：Xcode 分屏preprocess显示：
@try {} @finally {} __attribute__((objc_ownership(strong))) __typeof__(self) self = self_weak_;

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