valueness.cpp

template<typename T>
void f(T&& param);
// T is deduced so && means universal reference

void f(std::string&& param);
// No deduction involved so && means r-value reference

template<typename T>
void a(T&& param) { /*does something*/ }
  
template<typename T>
void b(T&& param) {
  // Since both are UR forward preserve valueness function 
  // `a` will receive a l or r value depending on the param
  // passed to `b`.
  a(std::forward<T>(param));
}