C# Indexer and Linq

Question

I have a property in a class:

public int this[int index]
        {
            get { return _desk[index]; }
            set { _desk[index] = value; }
        }

But I cant use this class in Linq. How to make it ?

Answer 1

An indexer doesn't automatically give you enumeration. In order to be able to call LINQ methods, you need to implement IEnumerable<int> on your class.

I'm assuming your _desk object is a simple array - if I'm wrong here and _desk is something other class that has an indexer, you may need to make that class implement IEnumerable<int> too.

You'd then need to do something like this:

public class Position : IEnumerable<int>
{
    private int[] _desk;

    public int this[int index]
    {
        get { return _desk[index]; }
        set { _desk[index] = value; }
    }

    /* the rest of your class */

    public IEnumerator<int> GetEnumerator()
    {
        return ((IEnumerable<int>)_desk).GetEnumerator();
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return _desk.GetEnumerator();
    }
}

I've no idea if the implementations of GetEnumerator() are best practice when wrapping an array, but they should work.

Answer 2

If your class doesn't implement IEnumerable<T> but has an indexer and a Count property, you can create an IEnumerable of indexes using the Enumerable.Range Method, and project each index to the collection item using the Enumerable.Select Extension Method:

var query = Enumerable.Range(0, obj.Count)
                      .Select(index => obj[index])
                      ...