using System;

public class Program

{

    public static void Main()

    {

        var x = new MyClassWithIndexer()

        {

            ["foo"] = 34,

            ["bar"] = 42,

            [10] = "Ten",

            [42] = "Meaning of life"

        };

    }

}

​

public class MyClassWithIndexer

    {

        public int this[string index]

        {

            set

            {

                Console.WriteLine($"Index: {index}, value: {value}");

            }

        }

        public string this[int index]

        {

            set

            {

                Console.WriteLine($"Index: {index}, value: {value}");

            }

        }

}