ForEachReferenceBenchmarks.cs

using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using System.Runtime.InteropServices;
using BenchmarkDotNet.Attributes;

public class ForEachReferenceBenchmarks
{
    string[]? array;
    List<string>? list;
    ImmutableArray<string>? immutableArray;

    [Params(10, 10_000)]
    public int Count { get; set; }

    [GlobalSetup]
    public void GlobalSetup()
    {
        var range = Enumerable.Range(0, Count).Select(x => x.ToString());
        array = range.ToArray();
        list = range.ToList();
        immutableArray = System.Collections.Immutable.ImmutableArray.Create(array);
    }

    [Benchmark(Baseline = true)]
    public int Array()
    {
        var sum = 0;
        foreach (var item in array!)
            sum += int.Parse(item);
        return sum;
    }

    [Benchmark]
    public int Array_AsSpan()
    {
        var sum = 0;
        foreach (var item in array!.AsSpan())
            sum += int.Parse(item);
        return sum;
    }

    [Benchmark]
    public int List()
    {
        var sum = 0;
        foreach (var item in list!)
            sum += int.Parse(item);
        return sum;
    }

    [Benchmark]
    public int List_AsSpan()
    {
        var sum = 0;
        foreach (var item in CollectionsMarshal.AsSpan(list!))
            sum += int.Parse(item);
        return sum;
    }

    [Benchmark]
    public int ImmutableArray()
    {
        var sum = 0;
        foreach (var item in immutableArray!)
            sum += int.Parse(item);
        return sum;
    }

}