How do I use composition with inheritance?

Question

I\'m going to try to ask my question in the context of a simple example...

Let\'s say I have an abstract base class Car. Car has-a basic Engine object. I have a method

Answer 1

You can use C# generics to get what you're looking for, here.

The distinction of using generics is that your Ferrari "knows" that its Engine is-a TurboEngine, while the Car class doesn't have to know anything new—only that EngineType is-an Engine.

class Program
{
    static void Main(string[] args)
    {
        Ferrari ferarri = new Ferrari();
        ferarri.Start();
        ferarri.Boost();
    }
}
public class Car where EngineType : Engine, new()
{
    protected EngineType engine;

    public Car()
    {
        this.CreateEngine();
    }
    protected void CreateEngine()
    {
        this.engine = new EngineType();
    }
    public void Start()
    {
        engine.Start();
    }
}

public class Ferrari : Car
{
    public void Boost()
    {
        engine.Boost();
    }
}

public class Engine
{
    public virtual void Start()
    {
        Console.WriteLine("Vroom!");
    }
}
public class TurboEngine : Engine
{
    public void Boost()
    {
        Console.WriteLine("Hang on to your teeth...");
    }
    public override void Start()
    {
        Console.WriteLine("VROOOOM! VROOOOM!");
    }
}