Benchmarking C# for vs for each statement (plus Span<T>)

Benchmarks.cs

using BenchmarkDotNet.Attributes;
using System.Runtime.InteropServices;
using BenchmarkDotNet.Order;

namespace AutoIndexCache.Benchmarks;

[MemoryDiagnoser]
[Orderer(SummaryOrderPolicy.FastestToSlowest)]
[GcServer]
public class Benchmarks
{
    [GlobalSetup]
    public void _GlobalSetup()
    {
        this.list = [];

        for (var i = 1; i <= 100_000; i++)
        {
            this.list.Add(new(i));
        }

        this.array = this.list.ToArray();
    }

    [Benchmark()]
    public Object Array_ForLoop()
    {
        var sum = 0L;
            
        for (int i = 0; i < this.array.Length; i++)
        {
            var user = this.array[i];
            sum += user.Id;
        }

        return sum;
    }

    [Benchmark()]
    public Object Array_ForLoop_LengthSaved()
    {
        var sum = 0L;
        var length = this.array.Length;

        for (int i = 0; i < length; i++)
        {
            var user = this.array[i];
            sum += user.Id;
        }

        return sum;
    }

    [Benchmark()]
    public Object Array_ForEachLoop()
    {
        var sum = 0L;
            
        foreach (var user in this.array)
        {
            sum += user.Id;
        }

        return sum;
    }

    [Benchmark()]
    public Object List_ForLoop()
    {
        var sum = 0L;
            
        for (int i = 0; i < this.list.Count; i++)
        {
            var user = this.list[i];
            sum += user.Id;
        }

        return sum;
    }

    [Benchmark()]
    public Object List_ForLoop_LengthSaved()
    {
        var sum = 0L;
        var length = this.list.Count;

        for (int i = 0; i < length; i++)
        {
            var user = this.list[i];
            sum += user.Id;
        }

        return sum;
    }

    [Benchmark()]
    public Object List_ForEachLoop()
    {
        var sum = 0L;
            
        foreach (var user in this.list)
        {
            sum += user.Id;
        }

        return sum;
    }

    [Benchmark()]
    public Object SpanFromArray_ForLoop()
    {
        var sum = 0L;
        var span = this.array.AsSpan();
            
        for (int i = 0; i < span.Length; i++)
        {
            var user = span[i];
            sum += user.Id;
        }

        return sum;
    }

    [Benchmark()]
    public Object SpanFromArray_ForLoop_LengthSaved()
    {
        var sum = 0L;
        var span = this.array.AsSpan();
        var length = span.Length;

        for (int i = 0; i < length; i++)
        {
            var user = span[i];
            sum += user.Id;
        }

        return sum;
    }

    [Benchmark()]
    public Object SpanFromArray_ForEachLoop()
    {
        var sum = 0L;
        var span = this.array.AsSpan();
            
        foreach (var user in span)
        {
            sum += user.Id;
        }

        return sum;
    }

    [Benchmark()]
    public Object SpanFromList_ForLoop()
    {
        var sum = 0L;
        var span = CollectionsMarshal.AsSpan(this.list);
            
        for (int i = 0; i < span.Length; i++)
        {
            var user = span[i];
            sum += user.Id;
        }

        return sum;
    }

    [Benchmark()]
    public Object SpanFromList_ForLoop_LengthSaved()
    {
        var sum = 0L;
        var span = CollectionsMarshal.AsSpan(this.list);
        var length = span.Length;

        for (int i = 0; i < length; i++)
        {
            var user = span[i];
            sum += user.Id;
        }

        return sum;
    }

    [Benchmark()]
    public Object SpanFromList_ForEachLoop()
    {
        var sum = 0L;
        var span = CollectionsMarshal.AsSpan(this.list);
            
        foreach (var user in span)
        {
            sum += user.Id;
        }

        return sum;
    }

    private Item[] array;
    private List<Item> list;

    private record Item(Int32 Id);
}