/in/foo.cc:10:8: error: field 'n' has incomplete type 'list'
  list(n);
        ^
/in/foo.cc:5:7: note: definition of 'class list' is not complete until the closing brace
 class list
       ^~~~
/in/foo.cc:10:8: error: redeclaration of '<typeprefixerror>list::n'
  list(n);
        ^
/in/foo.cc:7:6: note: previous declaration 'int list::n'
  int n;
      ^
/in/foo.cc:14:11: error: expected constructor, destructor, or type conversion before '(' token
 list::list(n)
           ^