Method operator<=>

Examples/NoModules/Chapter 20/Ex20_12A/Box.h:20–23

  double getHeight() const { return m_height; }

  std::partial_ordering operator<=>(const Box& otherBox) const 
  { 
    return volume() <=> otherBox.volume();
  }
  std::partial_ordering operator<=>(double otherVolume) const 
  { 
    return volume() <=> otherVolume;