Members not available when implementing IList

Question

I've tried to create a simple class implementing IList. However the members are not available unless I first cast DiskBackedCollection to IList. How can I make it usable without casting?

public partial class DiskBackedCollection<T> : IList<T>
{
    private List<T> _underlyingList = new List<T>();

    int IList<T>.IndexOf(T item)
    {
        return _underlyingList.IndexOf(item);
    }

    T IList<T>.this[int index]
    {
        get
        {
            return _underlyingList[index];
            throw new NotImplementedException();
        }
        set
        {
            throw new NotImplementedException();
        }
    }

    int ICollection<T>.Count
    {
        get
        {
            return _underlyingList.Count;
        }
    }

    IEnumerator<T> IEnumerable<T>.GetEnumerator()
    {
        return new DiskBackedCollectionEnumerator(this);
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return new DiskBackedCollectionEnumerator(this);
    }
}

[C# Interfaces. Implicit implementation versus Explicit implementation](http://stackoverflow.com/questions/143405/c-sharp-interfaces-implicit-implementation-versus-explicit-implementation). — poke, May 25 '13 at 13:50
And I managed to get into my head it was just a code clarity thing! - Thanks for the link. — Lee, May 25 '13 at 13:52
Not relevant to your question, but it will usually simplify your code to use the base class `Collection`, which has virtual methods `InsertItem`, `RemoveItem` etc that you can override for any custom functionality. — Joe, May 25 '13 at 15:24
@Joe To my knowledge the Collection class uses an internal List to store the items. So the class is best used for adding validation to a simple list. However as I'm going to be storing and retrieving the data from disk (many millions of rows), I don't want it to be stored in a list internally. From my implementation above you are correct, but it is far from complete. — Lee, May 26 '13 at 12:15
@Lee, you're right, except that to be pedantic, it uses an internal `IList`, which doesn't have to be a `List`. My comment was based on your implementation above (_underlyingList). — Joe, May 26 '13 at 16:19

score 2 · Accepted Answer · answered May 25 '13 at 13:48

2

It's because each of the members has IList<T>. in front of them. Remove that and they should show up.

Implementating the interface members with an IList<T>. in front of them is called explicit implementation.

answered May 25 '13 at 13:48

Zach Johnson

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@DaveShaw The compiler should complain if you don’t publicly implement an interface (in which case you technically wouldn’t have implemented it). – poke May 25 '13 at 13:53

score 0 · Answer 2 · answered May 25 '13 at 13:53

0

Your methods that implement interface requirements must be public. Yours are not.

Also, you need to remove your explicit implementation:

public int Count
{
  get
  {
    return _underlyingList.Count;
  }
}

answered May 25 '13 at 13:53

Matt Houser

33,983
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Members not available when implementing IList

2 Answers2