C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;

namespace TestByValue
{
    class Program
    {
        static void Main(string[] args)
        {
            Foo[] aArray = new Foo[3];
            aArray[0].Increment();

            Console.WriteLine("aArray[0].x is {0} and should be {1}", aArray[0].x, 1);
            Debug.Assert(aArray[0].x == 1);

            List<Foo> aList = new List<Foo>();
            aList.Add(new Foo());
            aList[0].Increment();

            Console.WriteLine("aList[0].x is {0} and should be {1}", aList[0].x, 1);
            Debug.Assert(aList[0].x == 1);      // This Assert fires
        }

        struct Foo
        {
            public int x;

            public void Increment()
            {
                x++;
            }
        }
    }
}