foo.cc: In member function ‘Vector3& Vector3::operator*(Vector3&)’:
foo.cc:35:24: warning: reference to local variable ‘v’ returned [-Wreturn-local-addr]
   35 |                 return v;
      |                        ^
foo.cc:31:25: note: declared here
   31 |                 Vector3 v;
      |                         ^