Question: As the title states, I would like to declare an indexer `object this[int index]` in an abstract class as an abstract member.

Is this possible in any way? Is it possible to declare this in an interface too?

Answer: 
[Of course](http://ycouriel.blogspot.com/2009/10/c-abstract-index-operator.html): 

```
public abstract class ClassWithAbstractIndexer 
{
    public abstract int this[int index]
    {
        get;
        set;
    }
}

```
You may declare it like this:

```
internal abstract class Hello
{
  public abstract int Indexer[int index]
  {
      get;
  }
}

```

Then you'll have the option to override only `get` or override both `get` and `set`.