foreach (var item in items) {}

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

namespace ArrayTest
{
    public class Foo
    {
        public string Bar1 { get; set; }
        public string Bar2 { get; set; }
        public string Bar3 { get; set; }
        public string Bar4 { get; set; }
        public string Bar5 { get; set; }
    }

    class Program
    {
        const int Size = 10000000;
        static readonly List<string> Output = new List<string>();
        static readonly List<string> Print = new List<string>();

        static void Main()
        {
            var foo1 = GetFoo1();
            var foo2 = GetFoo2();

            UseArray(foo1);
            UseIEnumerable(foo2);

            // Get random element from the list. Just for avoiding compiler optimization.
            int i = new Random().Next(Output.Count);
            Console.WriteLine(Output[i]);

            foreach (string o in Print)
            {
                Console.WriteLine(o);
            }
        }

        private static void WriteLine(string x)
        {
            Output.Add(x);
        }

        private static Foo[] GetFoo1()
        {
            Stopwatch sw = Stopwatch.StartNew();
            var foo1 = new Foo[Size];
            for (int i = 0; i < Size; i += 1)
            {
                var foo = new Foo { Bar1 = "Bar1", Bar2 = "Bar2", Bar3 = "Bar3", Bar4 = "Bar4", Bar5 = "Bar5" };
                foo1[i] = foo;
            }
            sw.Stop();
            Print.Add(string.Format("CreateArray: {0}", sw.ElapsedMilliseconds));
            return foo1;
        }

        private static IEnumerable<Foo> GetFoo2()
        {
            Stopwatch sw = Stopwatch.StartNew();
            for (int i = 0; i < Size; i += 1)
            {
                var foo = new Foo {Bar1 = "Bar1", Bar2 = "Bar2", Bar3 = "Bar3", Bar4 = "Bar4", Bar5 = "Bar5"};
                yield return foo;
            }
            sw.Stop();
            Print.Add(string.Format("CreateIEnumerable: {0}", sw.ElapsedMilliseconds));
        }

        static void UseArray<T>(T[] values)
        {
            Stopwatch sw = Stopwatch.StartNew();
            var count = values.Length;
            foreach (object o in values)
            {
                var x = (Foo)o;
                WriteLine(x.Bar1);
            }
            sw.Stop();
            Print.Add(string.Format("UseArray: {0}, count: {1}", sw.ElapsedMilliseconds, count));
        }

        static void UseIEnumerable<T>(IEnumerable<T> values)
        {
            Stopwatch sw = Stopwatch.StartNew();
            var count = values.Count();
            foreach (object o in values)
            {
                var x = (Foo)o;
                WriteLine(x.Bar1);
            }
            sw.Stop();
            Print.Add(string.Format("UseIEnumerable: {0}, count: {1}", sw.ElapsedMilliseconds, count));
        }
    }
}