using System;

public class Program

{

    public static void Main()

    {

        var c = new MyClass();

        Console.WriteLine(c["test", DateTime.Now]);

        c["test", DateTime.Now] = 5;

    }

}

​

public class MyClass

{

    public int this[string s, DateTime dt]

    {

        get { return 42; }

        set { Console.WriteLine("Setting value of ({0}, {1}) to: {2}", s, dt, value); }

    }

}