using System;

using System.Collections.Generic;

using System.Linq;

​

namespace ForeachTest

{

    internal class Program

    {

        static void Main(string[] args)

        {

            var data1 = MyClass.GetData1();

            foreach (var item in data1)

                item.Message = "New Message";

​

            foreach (var item in data1)

                Console.WriteLine(item.Message);

​

            // ----------------------------------------

​

            var data2 = MyClass.GetData2();

​

            foreach (var item in data2)

                item.Message = "New Message";

​

            foreach (var item in data2)

                Console.WriteLine(item.Message);

        }

    }

}

​

public class MyClass

{

    public string Message { get; set; }

​

    public MyClass(string message) => Message = message;

​

    public static IEnumerable<MyClass> GetData1()

    {

        var data = new string[] { "Old Message 1", "Old Message 2", "Old Message 3" };

​

        return data.Select(x => new MyClass(x));

    }

​

    public static IEnumerable<MyClass> GetData2()

    {

        var data = new MyClass[] {

            new MyClass("Old Message 1"),

            new MyClass("Old Message 2"),

            new MyClass("Old Message 3")

        };

​

        return data;

    }

}