Implementing indexing “operator” in on a class in C#

Question

How would one go about implementing the indexing "operator" on a class in C#?

class Foo {

}

Foo f = new Foo();
f["key"] = "some val";
f["other key"] = "some other val";

in C#? Searched MSDN but came up empty.

Answer 1

Here is an example using a dictionary as storage:

public class Foo {

    private Dictionary<string, string> _items;

    public Foo() {
        _items = new Dictionary<string, string>();
    }

    public string this[string key] {
        get {
            return _items[key];
        }
        set {
            _items[key]=value;
        }
    }

}

Answer 2

    private List<string> MyList = new List<string>();
    public string this[int i]
    {
        get
        {
            return MyList[i];
        }
        set
        {
            MyList[i] = value;
        }

    }

You can define several accessors for different types (ie string instead of int for example) if it's needed.

Answer 3

There called Indexers or sometimes Indexer Properties.

Here's the MSDN page about them.