RefQualified.cpp

struct Foo {
  // used when Foo instance is an l-value
  void operator()() const & {
    std::cout << "l-value" << "\n";
  }

  // used when Foo isntance is an r-value
  void operator()() const && {
    std::cout << "r-value" << "\n";
  }
};

Foo f;
f(); // First operator is used
Foo()(); // Second operator is used