using System.Diagnostics;

using System.Linq;

using System;

​

var sw = Stopwatch.StartNew();

var list1 = Enumerable

            .Range(1, 2)

            .Select(n => Random.Shared.Next());

sw.Stop();

Console.WriteLine($"Just IEnumerable: {sw.ElapsedMilliseconds}ms");

​

var sw2 = Stopwatch.StartNew();

var list2 = Enumerable

            .Range(1, 2)

            .Select(n => Random.Shared.Next())

            .ToList();

sw2.Stop();

Console.WriteLine($"IEnumerable.ToList(): {sw2.ElapsedMilliseconds}ms");

​

var sw3 = Stopwatch.StartNew();

var list3 = Enumerable

            .Range(1, 2)

            .Select(n => Random.Shared.Next());

sw3.Stop();

Console.WriteLine($"Just IEnumerable#2: {sw3.ElapsedMilliseconds}ms");