Class or Enum to restrict function parameter to list of valid values c#

Question

Let's say I have something like: Vehicles.
Below Vehicles I have Cars, Trucks and Pickups.
Below Cars I only have BMW and Toyota.

Now I want to call something like:

if (NumberOfSeats(Vehicles.Cars.Toyota) {}

So NumberOfSeats should be restricted to only receive BMW and Toyota:

public int NumberOfSeats(??) { return 4;}

But it should give a compile time error if I call:

if (NumberOfSeats(Vehicles.Cars.Yamaha) {}

Furthermore I would like to have a method to BMW, that will return a string value (let'say Name() )

Should my class composition be looking at Enums, Classes, Inheritance or combination?

Answer 1

I guess you are thinking in backwards. My way of thinking is to create analogy between real-world objects and software classes (This is my way oıf Object Oriented thinking).

When I consider a real-world scenario there is no such thing as "number of seats" in the world itself. It is a property of a vehicle. Cars have this property buses have this property, Cars usually have 4 (or 5) seats, buses have 45 etc.

So I would implement it as a property of a vehicle ot a self method. This way it will be more meaningful. Such as:

public interface IVehicle
{
    int NumberOfSeats { get; }
    string Brand { get; set; }
}

public class Car : IVehicle
{
    public int NumberOfSeats { get; private set; }
    public string Brand { get; set; }

    public Car(int noofseats, string brand)
    {
        this.NumberOfSeats = noofseats;
        this.Brand = brand;
    }
}

Car bmw = new Car(4, "BMW");
Car toyota = new Car(4, "Toyota");
Car qashqai = new Var(7, "Nissan");