using System.Collections;

using System.Collections.Generic;

​

public interface IHasParts<TCollectionType> where TCollectionType : ICollection

{

  TCollectionType Parts { get; set; }

}

​

public class CarPart

{

  //...

}

​

public class Car : IHasParts<List<CarPart>>

{

  public List<CarPart> Parts { get; set; }

  //...

}

public class Program

{

    public static void Main()

    {

        Car c = new Car() {

            Parts = new List<CarPart>() {

                // ...

            }

        };

​

        object o = (object)c;

​

        int partsCount = ((IHasParts<ICollection>)o).Parts.Count; // InvalidCastException

    }

}