How to use generic?

Question

I wont to use only one method to unbox like this:

public interface IModule<T, U>
  where T : BaseBox
  where U : BaseItem
{
  U[] GetItems<T>( int id );
}

public sealed partial class Module<T, U> : IModule<T, U>
  where T : BaseBox
  where U : BaseItem
{
  U[] IModule<T, U>.GetItems<T>( int id )
  {
    return T.Unboxing(); // It is wrong!
  }
}

But I can't. How do I have to write right generics?

Next code to understand.I have item's types:

public abstract class BaseItem
{
  protected int _id;
  protected string _description;
}

public sealed class TriangleItem : BaseItem
{
  public int TriangleId { get { return _id; } set { _id = value; } }
  public string TriangleDescription { get { return _description; } set { _description = value; } }
  public Color color { get; set; }
}

public sealed class CircleItem : BaseItem
{
  public int CircleId { get { return _id; } set { _id = value; } }
  public string CircleDescription { get { return _description; } set { _description = value; } }
  public int Radius { get; set; }
}

Then I have boxes for items:

public abstract class BaseBox
{
  public string ItemsXml { get; set; }
  public abstract BaseItem[] Unboxing();
}

public sealed class TriangleBox : BaseBox
{
  public TriangleItem[] Unboxing()
  {
    return Util.FromXml( ItemsXml ).Select( i => new TriangleItem { TriangleId = int.Parse( i ), TriangleDescription = i, Color = Color.Red } ).ToArray();
  }
}

public sealed class CircleBox : BaseBox
{
  public CircleItem[] Unboxing()
  {
    return Util.FromXml( ItemsXml ).Select( i => new CircleItem { CircleId = int.Parse( i ), CircleDescription = i, Radius = 5 } ).ToArray();
  }
}

Here I have different implementations Unboxing-method.

Answer 1

As Sayse mentioned in the comment, you are trying to use T as a static method and need an instance. For example,

public sealed partial class Module<T, U> : IModule<T, U>
  where T : BaseBox
  where U : BaseItem
{
    private T _box;

    public Module(T box)
    {
        _box = box;
    }

    U[] IModule<T, U>.GetItems<T>( int id )
    {
        // You need to determine how id relates to _box.
        return _box.Unboxing();
    }
}