c# – How to sort an array by type?

Question:

There is an array of objects derived from the Car class: PassengerCar , FreightCar , and SpecializedFreightCar .

You need to sort the array by the types of heirs. For example, PassengerCar objects come first, then FreightCar , then SpecializedFreightCar .

PassengerCar and FreightCar inherit traits from the Car class.

SpecializedFreightCar inherits traits from the FreightCar class.

Answer:

If sorting can be used in multiple places, I recommend writing a Comparer, like so:

class CarComparer : IComparer<Car>
{
    static Dictionary<Type, int> priorities = new Dictionary<Type, int>();
    static CarComparer()
    {
        priorities.Add(typeof(PassengerCar), 1);
        priorities.Add(typeof(FreightCar), 2);
        priorities.Add(typeof(SpecializedFreightCar), 3);
    }

    int PriorityFor(Type type)
    {
        priorities.TryGetValue(type, out int p);
        return p;
    }

    public int Compare(Car x, Car y)
    {
        int priorityX = PriorityFor(x.GetType());
        int priorityY = PriorityFor(y.GetType());
        return priorityX.CompareTo(priorityY);
    }
}

Usage example:

Car[] cars =
{
    new SpecializedFreightCar(),
    new FreightCar(),
    new FreightCar(),
    new PassengerCar(),
    new SpecializedFreightCar()
};
Array.Sort(cars, new CarComparer());
Console.WriteLine(string.Join<Car>("\n", cars));

Code copied almost verbatim from Agile Principles, Patterns, and Techniques in C# by Robert Martin, Mika Martin