如何为接口定义索引器行为？

Question

Is it possible to add the indexer behaviour from an interface?

something like this :

interface IIndexable<T>
{
   T this[string index];
}

Answer 1

Yes, it is possible. In fact, all you're missing is the getter/setter on your indexer. Just add it as follows:

interface IIndexable<T>
{
     T this[string index] {get; set;}
}

Answer 2

From MSDN :

public interface ISomeInterface
{
    //...

    // Indexer declaration:
    string this[int index]
    {
        get;
        set;
    }
}

Indexers can be declared on an interface (C# Reference). Accessors of interface indexers differ from the accessors of class indexers in the following ways:

• Interface accessors do not use modifiers.
• An interface accessor does not have a body.

Answer 3

A bit more generic interface (taken from IDictionary<,> ), would be:

interface IIndexable<TKey, TValue>
{
    TValue this[TKey key] { get; set; }
}

I only wonder why they didn't include it in mscorlib, so that IDictionary could implement it. It would've made sense.