example-b.cpp

class A {
  std::vector<std::string> _values;
public:
  void addValue(const std::string &val) {
    // some logic
    _values.emplace_back(val);
  }
  
  void addValue(std::string &&val) { // r-value ref overload
    // some logic
    _values.emplace_back(std::move(val)); // We know that is a r-value
  }
};

// Not only overload resolution will be able to pick the r-value overload for calls being made with r-value arguments,
// but we will be also allowed to use this when we know is the last usage of a value. Example
A a;

for (...) {
  std::string s = compute(...);
  a.addValue(std::move(s)); // Since is the last use of s, it is safe and more efficient to just move.
}