using System;

using System.Linq;

using System.Runtime.InteropServices;

​

namespace ConsoleApp3

{

    class Program

    {

        static void Main(string[] args)

        {

            var s = new MutableStruct();

            var span = MemoryMarshal.CreateReadOnlySpan(ref s, 1);

            var byteSpan = MemoryMarshal.Cast<MutableStruct, byte>(span);

​

            Console.WriteLine(string.Join("", byteSpan.ToArray().Select(v => $"{v:X2}"))); // 00000000

​

            s.SetX(42);

            Console.WriteLine(string.Join("", byteSpan.ToArray().Select(v => $"{v:X2}"))); // 2A0000000

        }

    }

​

    struct MutableStruct

    {

        private int _x;

        public int X => _x;

        public void SetX(int value) => _x = value;

    }

}

​