foo.cc: In member function 'xl& xl::jf(xl&)':
foo.cc:54:10: warning: reference to local variable 'nw' returned [-Wreturn-local-addr]
   54 |   return nw;
      |          ^~
foo.cc:47:6: note: declared here
   47 |   xl nw(*this);
      |      ^~

[Hydro](https://hydro.ac)提供评测服务