IList<Type> to IList<BaseType>

Question

I have a few classes:

class Vehicle
{
}

class Car : Vehicle
{
}

I have a list of the derived class: IList<Car> cars;

I would like to convert the list to its base class, and have tried: IList<Vehicle> baseList = cars as IList<Vehicle>;

But I always get null. Also

cars is IList<Vehicle> evaluates to be false.

Granted, I can add the items to a list if I do the following:

List<Vehicle> test = new List<Vehicle> ();

foreach ( Car car in cars )
{
   test.Add(car);
}

And I get my list, but I know there has to be a better way. Any thoughts?

Answer 1

Use IEnumerable<T>.Cast :

IList<Vehicle> vehicles = cars.Cast<Vehicle>().ToList();

Alternatively, you may be able to avoid the conversion to List depending on how you wish to process the source car list.

Answer 2

That sort of polymorphism that lets you cast IList<Car> to IList<Vehicle> is unsafe, because it would let you insert a Truck in your IList<Car>.

Answer 3

You're facing the problem that there is limited co- and contravariance in C#. There is an interesting approach in C# 4.0, described here at the very ending. However, it creates some other limitations that are related to the truck-problem in the answer from Novelocrat.

Answer 4

Here are a couple of approaches using Linq:

IList<Derived> list = new List<Derived>();
list.Add(new Derived());

IList<Base> otherlist = new List<Base>(from item in list select item as Base);
IList<Base> otherlist2 = new List<Base>(list.Select(item => item as Base));

Answer 5

You can also take a look on Krzysztof's Cwalina article, Simulated Covariance for .NET Generics