/in/foo.cc: In member function 'void Activity::run()':
/in/foo.cc:53:24: error: cannot call member function 'void Resource::use(int)' without object
         Resource::use(1);
                        ^
/in/foo.cc:55:28: error: cannot call member function 'void Resource::release(int)' without object
         Resource::release(1);
                            ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:63:14: warning: unused variable 'resource' [-Wunused-variable]
     Resource resource;
              ^~~~~~~~