C++ Primer Plus

An Implementation Comment

The implementation described in the preceding sections stores both rectangular and polar coordinates for a vector in the Vector object. However, the public interface doesn’t depend on this fact. All the interface calls for is that both representations can be displayed and that individual values can be returned. The internal implementation could be quite different. As mentioned earlier, the object could store just the x and y components. Then, say, the magval() method, which returns the value of the magnitude of the vector, could calculate the magnitude from the x and y values instead of just looking up the value as stored in the object. Such an approach changes the implementation but leaves the user interface unchanged. ...