小编YZ_*_*_SO的帖子

\xc2\xa710.4/3详细给出了 decl-reachable 所有可能的情况。然而，我无法完全理解它。考虑\xc2\xa710.4/6中描述的示例：

Source file "foo.h":\n  namespace N {\n  struct X {};\n  int d();\n  int e();\n  inline int f(X, int = d()) { return e(); }\n  int g(X);\n  int h(X);\n}\n\nModule M interface:\nmodule;\n#include "foo.h"\nexport module M;\ntemplate<typename T> int use_f() {\n  N::X x;                       // N\xe2\x80\x8b::\xe2\x80\x8bX, N, and \xe2\x80\x8b::\xe2\x80\x8b are decl-reachable from use_\xc2\xadf\n  return f(x, 123);             // N\xe2\x80\x8b::\xe2\x80\x8bf is decl-reachable from use_\xc2\xadf,\n                                // N\xe2\x80\x8b::\xe2\x80\x8be is indirectly decl-reachable from use_\xc2\xadf\n                                //   because it is decl-reachable from N\xe2\x80\x8b::\xe2\x80\x8bf, and\n                                // N\xe2\x80\x8b::\xe2\x80\x8bd …