Challenge: Implement Inheritance Hierarchy

Problem statement

Let’s modify RailwayVehicle. In addition to reporting the distance that it advances, let’s have it also make sounds. To keep the output short, let’s print the sounds per 100 kilometers:

class RailwayVehicle {
    void advance(size_t kilometers) {
        writefln("The vehicle is advancing %s kilometers", kilometers);

        foreach (i; 0 .. kilometers

...