Question

I have a class which must implement the following property

public ICollection<IType> Items
{
     get { return this.items;}
}

My question is how to implement this when the type of this.items is a List<MyType> where MyType implements IType. I need to ensure the following:

1. Unecessary enumeration of the list is avoided if possible
2. That the class can internally treat the elements of this.items as their concrete type
3. That external callers may add and remove elements to this collection

Thanks in advance.

Answer 1

How about Items being IEnumerable<IType>? IEnumerable is covariant so the code would just work with no changes. On the other hand, you could have another, dedicated method to add elements to the internal list.

class MainClass
{
  public static void Main()
  {
    ShowMeHowToDoIt show = new ShowMeHowToDoIt();
    show.Add( new TheType() );

    foreach ( var item in show.Items )
    {
   Console.WriteLine( item );
    }     
  }
}

public class ShowMeHowToDoIt
{
  private List<TheType> items = new List<TheType>();

  public void Add( TheType item ) { items.Add( item ); }

  public IEnumerable<IType> Items
  {
    get { return items; }
  }
}

public interface IType { }

public class TheType : IType { }