.NET Benchmark for comparing iteration using foreach over ArrayList vs List<T> containing Reference Type

ArrayList_foreach_vs_List(Person)_foreach_ReferenceType_Benchmarks.linq

[MemoryDiagnoser]
[GroupBenchmarksBy(BenchmarkLogicalGroupRule.ByCategory)]
[CategoriesColumn]
[Config(typeof(IterationBenchmarks.IterationBenchmarksConfig))]
public class IterationBenchmarks
{
	[Params(1_000, 10_000, 50_000)]
	public int Count;

	private ArrayList _arrayList = null;
	private List<Person> _listOfPerson = null;
	private Consumer _consumer = null;

	[GlobalSetup]
	public void GlobalSetup()
	{
		_arrayList = new ArrayList(Count);
		_listOfPerson = new List<Person>(Count);
		for (int i = 0; i < Count; i++)
		{
			Person p = new Person(i, "Dwight Schrute");
			_arrayList.Add(p);   // boxed
			_listOfPerson.Add(p);
		}

		_consumer = new Consumer();
	}

	[Benchmark(Baseline = true, Description = "ArrayList<Person> foreach")]
	[MethodImpl(MethodImplOptions.NoInlining)]
	public void ArrayList_Foreach()
	{
		foreach (object item in _arrayList)
		{
			IPerson value = (Person)item; // unbox
			_consumer.Consume(value);
		}
	}

	[Benchmark(Description = "List<Person> foreach")]
	[MethodImpl(MethodImplOptions.NoInlining)]
	public void List_Foreach()
	{
		foreach (IPerson p in _listOfPerson)
		{
			_consumer.Consume(p);
		}
	}

	private class IterationBenchmarksConfig : ManualConfig
	{
		public IterationBenchmarksConfig()
		{
			SummaryStyle = BenchmarkDotNet.Reports.SummaryStyle.Default.WithRatioStyle(RatioStyle.Trend);
		}
	}
}

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

public interface IPerson
{
	int Compute();
}

public class Person : IPerson
{
	public readonly int Id;
	public readonly string Name;

	public Person(int id, string name)
	{
		Id = id;
		Name = name;
	}

	public int Compute()
	{
		// Cheap deterministic work; no allocations; good for net48 + net8.
		Random rand = new Random();
		int x = rand.Next() ^ (Id * 397);
		x = (x << 5) | (int)((uint)x >> 27);
		x = x * 31 + Id;
		return x;
	}
}

Results_NET_10.0.102.txt

//	Run time: 00:04:25 (265.3 sec), executed benchmarks: 6
// * Summary *
//
//	BenchmarkDotNet v0.15.8, Windows 11 (10.0.26200.7628/25H2/2025Update/HudsonValley2)
//	AMD Ryzen 9 7945HX with Radeon Graphics 2.50GHz, 1 CPU, 32 logical and 16 physical cores
//
//	.NET SDK 10.0.102
//  [Host] : .NET 10.0.2 (10.0.2, 10.0.225.61305), X86 RyuJIT x86-64-v4
//
//| Method                      | Count | Mean       | Error     | StdDev    | Ratio        | RatioSD | Allocated | Alloc Ratio |
//|---------------------------- |------ |-----------:|----------:|----------:|-------------:|--------:|----------:|------------:|
//| 'ArrayList<Person> foreach' | 1000  |   5.489 μs | 0.1093 μs | 0.2682 μs |     baseline |         |      28 B |             |
//| 'List<Person> foreach'      | 1000  |   1.414 μs | 0.0282 μs | 0.0664 μs | 3.89x faster |   0.26x |         - |          NA |
//|                             |       |            |           |           |              |         |           |             |
//| 'ArrayList<Person> foreach' | 10000 |  52.598 μs | 1.0151 μs | 0.8998 μs |     baseline |         |      28 B |             |
//| 'List<Person> foreach'      | 10000 |  13.761 μs | 0.2710 μs | 0.6336 μs | 3.83x faster |   0.18x |         - |          NA |
//|                             |       |            |           |           |              |         |           |             |
//| 'ArrayList<Person> foreach' | 50000 | 262.266 μs | 5.0160 μs | 5.9711 μs |     baseline |         |      30 B |             |
//| 'List<Person> foreach'      | 50000 |  69.129 μs | 1.3808 μs | 2.1086 μs | 3.80x faster |   0.14x |         - |          NA |

Results_NETFramework_4.8.1.txt

//	Run time: 00:04:54 (294.4 sec), executed benchmarks: 6
// * Summary *
//
//	BenchmarkDotNet v0.15.8, Windows 11 (10.0.26200.7628/25H2/2025Update/HudsonValley2)
//	AMD Ryzen 9 7945HX with Radeon Graphics 2.50GHz, 1 CPU, 32 logical and 16 physical cores
//
//  [Host]     : .NET Framework 4.8.1 (4.8.9221.0), X86 LegacyJIT
//  DefaultJob : .NET Framework 4.8.1 (4.8.9221.0), X86 LegacyJIT
//
//| Method                      | Count | Mean       | Error     | StdDev     | Ratio        | RatioSD | Gen0   | Allocated | Alloc Ratio |
//|---------------------------- |------ |-----------:|----------:|-----------:|-------------:|--------:|-------:|----------:|------------:|
//| 'ArrayList<Person> foreach' | 1000  |   6.434 μs | 0.1274 μs |  0.2875 μs |     baseline |         | 0.0153 |      28 B |             |
//| 'List<Person> foreach'      | 1000  |   3.182 μs | 0.0627 μs |  0.1162 μs | 2.02x faster |   0.12x |      - |         - |          NA |
//|                             |       |            |           |            |              |         |        |           |             |
//| 'ArrayList<Person> foreach' | 10000 |  66.098 μs | 1.3836 μs |  3.9699 μs |     baseline |         |      - |      28 B |             |
//| 'List<Person> foreach'      | 10000 |  31.653 μs | 0.6145 μs |  1.3227 μs | 2.09x faster |   0.15x |      - |         - |          NA |
//|                             |       |            |           |            |              |         |        |           |             |
//| 'ArrayList<Person> foreach' | 50000 | 317.880 μs | 6.3573 μs | 14.3494 μs |     baseline |         |      - |      28 B |             |
//| 'List<Person> foreach'      | 50000 | 151.201 μs | 3.0140 μs |  5.8787 μs | 2.11x faster |   0.12x |      - |         - |          NA |