ToList(capacity) Benchmark

Program.cs

using BenchmarkDotNet.Running;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Jobs;

BenchmarkRunner.Run<BM>();

[SimpleJob(RuntimeMoniker.Net80, baseline: true)]
[SimpleJob(RuntimeMoniker.Net70)]
[SimpleJob(RuntimeMoniker.Net48)]
[MemoryDiagnoser(displayGenColumns: false)]
[HideColumns("Job", "Error", "StdDev", "Median", "RatioSD", "Alloc Ratio")]
public class BM {

    [Benchmark]
    public int[] ToArray() =>
        GetData().Where(static n => n % 4 == 0).ToArray();

    [Benchmark]
    public List<int> ToList() =>
        GetData().Where(static n => n % 4 == 0).ToList();

    [Benchmark]
    public List<int> ToListWithCapacity() =>
        GetData().Where(static n => n % 4 == 0).ToList(capacity: 25_000);

    private IEnumerable<int> GetData() {
        for (int i = 0; i < 100_000; i++) {
            yield return i;
        }
    }
}

public static class Extensions {

    public static List<TSource> ToList<TSource>(this IEnumerable<TSource> source, int capacity) {
        if (source is null) {
            throw new ArgumentNullException(nameof(source));
        }
        if (capacity < 0) {
            throw new ArgumentOutOfRangeException(nameof(capacity), "Non-negative number required.");
        }

        var list = new List<TSource>(capacity);
        list.AddRange(source);
        return list;
    }
}

BenchmarkDotNet v0.13.8, Windows 11 (10.0.22621.2361/22H2/2022Update/SunValley2)
AMD Ryzen 9 3900X, 1 CPU, 24 logical and 12 physical cores
.NET SDK 8.0.100-rc.1.23455.8
  [Host]             : .NET 8.0.0 (8.0.23.41904), X64 RyuJIT AVX2
  .NET 7.0           : .NET 7.0.11 (7.0.1123.42427), X64 RyuJIT AVX2
  .NET 8.0           : .NET 8.0.0 (8.0.23.41904), X64 RyuJIT AVX2
  .NET Framework 4.8 : .NET Framework 4.8.1 (4.8.9181.0), X64 RyuJIT VectorSize=256

| Method | Runtime | Mean | Ratio | Allocated |
|------------------- |------------------- |---------:|------:|----------:|-
| ToArray | .NET 7.0 | 653.0 μs | 2.66 | 226.41 KB |
| ToArray | .NET 8.0 | 244.9 μs | 1.00 | 226.41 KB |
| ToArray | .NET Framework 4.8 | 699.6 μs | 2.86 | 354.47 KB |
| | | | | |
| ToList | .NET 7.0 | 648.9 μs | 2.62 | 256.44 KB |
| ToList | .NET 8.0 | 247.9 μs | 1.00 | 256.44 KB |
| ToList | .NET Framework 4.8 | 692.2 μs | 2.80 | 256.88 KB |
| | | | | |
| ToListWithCapacity | .NET 7.0 | 730.3 μs | 3.05 | 97.81 KB |
| ToListWithCapacity | .NET 8.0 | 239.2 μs | 1.00 | 97.81 KB |
| ToListWithCapacity | .NET Framework 4.8 | 719.1 μs | 3.01 | 97.93 KB |