CollectionBenchmarks.cs

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

namespace ConcreteVsAbstract
{
    class Program
    {
        static void Main(string[] args) => BenchmarkRunner.Run<Benchmarks>();
    }

    [MemoryDiagnoser]
    public class Benchmarks
    {
        [Params(2, 10, 100, 1000, 10000)]
        public int Size;

        private int[] array;

        [GlobalSetup]
        public void Setup() => array = Enumerable.Range(0, Size).ToArray();

        [Benchmark]
        public int IterateOverConcreteArray()
        {
            int[] concrete = array;

            int result = 0;
            for (int i = 0; i < concrete.Length; i++)
                result += concrete[i];

            return result;
        }

        [Benchmark]
        public int IterateOverArrayAsIReadonlyList()
        {
            IReadOnlyList<int> abstraction = array;

            int result = 0;
            for (int i = 0; i < abstraction.Count; i++)
                result += abstraction[i];

            return result;
        }
    }
}