How to convert a generic List<T> to an Interface based List<T>

Question

I am sure I am missing something simple, however I am trying to convert a strongly typed list of objects that all implement an interface in to a list of that interface type.

Below is a sample to demonstrate the error:

public void ExampleCode(){
    List<Cube> cubes = new List<Cube>();
    List<Shape> allShapes;
    allShapes = cubes;//Syntax Error
    allShapes = (List<Shape>)cubes;//Syntax Error  
}

public class Cube : Shape
{
    public int ID { get; set; }
    public int Sides { get; set; }
}

public interface Shape
{
  int ID { get; set; }
  int Sides { get; set; }
}

Answer 1

Instead of casting like that, try:

allShapes = cubes.Cast<Shape>().ToList();

You need .NET 3.5 for this. I believe the Cast extension method can be found in System.Linq.