List vs Array

ListArrayIEnumerable.cs

using System.Collections.Generic;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

namespace ConsoleApp2 {
    [LegacyJitX64Job, LegacyJitX86Job, RyuJitX64Job]
    public class Benchmark {
        [Params(10, 100, 1000, 10000, 100000, 1000000)]
        public int ItemsCount { get; set; }

        public int[] array;
        public List<int> list;

        [IterationSetup]
        public void IterationSetup() {
            array = new int[ItemsCount];
            list = new List<int>(array);
        }

        [Benchmark(Baseline = true)]
        public int ForEachArrayAsArray() => ForEachArrayAsArrayCore(array);

        [Benchmark]
        public int ForEachArrayAsIEnumerable() => ForEachAsIEnumerableCore(array);

        [Benchmark]
        public int ForEachListAsList() => ForEachListAsListCore(list);

        [Benchmark]
        public int ForEachListAsIEnumerable() => ForEachAsIEnumerableCore(list);


        int ForEachArrayAsArrayCore(int[] a) {
            int sum = 0;
            foreach (int i in a) {
                sum += i;
            }
            return sum;
        }

        int ForEachAsIEnumerableCore(IEnumerable<int> a) {
            int sum = 0;
            foreach (int i in a) {
                sum += i;
            }
            return sum;
        }

        int ForEachListAsListCore(List<int> a) {
            int sum = 0;
            foreach (int i in a) {
                sum += i;
            }
            return sum;
        }
    }

    class Program {
        static void Main(string[] args) {
            BenchmarkRunner.Run<Benchmark>();
        }
    }
}