using System;

​

struct MyStruct

{

    public int value;

}

​

class MutableArray<T> where T : struct

{

    T[] a = new T[1];

    public ref T this[int i]

    {

        get { return ref a[i]; }

        //set { a[i] = value; }

    }

}

public class Program

{

    public static void Main()

    {

        var a = new MutableArray<MyStruct>();

        a[0].value = 22;

        Console.WriteLine(a[0].value);

    }

}