std::string line; // cannot be const
std::getline(std::cin, line);
// line should be const from here on out

std::string f1();
std::string f2(std::string s);
std::string f3() {
  const std::string s = f1(); // s is not meant to be modified
  // but I still want the move optimization here:
  const std::string result = f2(std::move(s)); // this doesn't move
  // and I want the compiler to move out here:
  return result; // this will probably RVO, but if not, the move
                 // constructor will not be used due to the const
}