using System;

​

public class Program

{

    public static void Main()

    {

        var int_string = new DoubleIndexer<int, string>();

        int_string["Hello"] = 1;

        ((IIndex<int, string>)int_string)[1] = "Hello";

        var int_byte = new DoubleIndexer<int, byte>();

        int_byte[1] = 134567;

        ((IIndex<int, byte>)int_byte)[134567] = 41;

        var int_int = new DoubleIndexer<int, int>();

        int_int[1] = 1345; // OK

        ((IIndex<int, int>)int_int)[13] = 5431;

    }

​

    public interface IIndex<T1, T2>

    {

        T2 this[T1 key] { get; set; }

    }

​

    internal class DoubleIndexer<T1, T2> : IIndex<T1, T2>

    {

        public T1 this[T2 key]

        {

            get => default;

            set

            {

                Console.WriteLine($"this[{key}] = {value}");

            }

        }

​

        T2 IIndex<T1, T2>.this[T1 key]

        {

            get => default;

            set

            {

                Console.WriteLine($"IIndex<{typeof(T1).Name}, {typeof(T2).Name}>.this[{key}] = {value}");

            }

        }

    }

}