ListInitializerBenchmark.cs

using System.Collections.Generic;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Jobs;
using Benchmarks.Mocks;

namespace Benchmarks;

[SimpleJob(RuntimeMoniker.Net70)]
[MeanColumn, MemoryDiagnoser]
public class ListInitializerBenchmark
{
    [Benchmark]
    public int AddRange()
    {
        var list = new List<ClassMock>();
        list.AddRange(_values);
        return list.Count;
    }
    
    [Benchmark]
    public int AsEnumerable()
    {
        var list = new List<ClassMock>(_values);
        return list.Count;
    }

    [Benchmark(Baseline = true)]
    public int Initializer()
    {
        var values = _values;
        var list = new List<ClassMock>
        {
            values[0],
            values[1],
            values[2],
            values[3],
            values[4],
        };

        return list.Count;
    }

    [Benchmark]
    public int WithoutInitializer()
    {
        var values = _values;
        var list = new List<ClassMock>();

        list.Add(values[0]);
        list.Add(values[1]);
        list.Add(values[2]);
        list.Add(values[3]);
        list.Add(values[4]);

        return list.Count;
    }

    private ClassMock[] _values = null!;

    [GlobalSetup]
    public void Init()
    {
        _values = new ClassMock[5];
        for (var i = 0; i < _values.Length; i++)
        {
            _values[i] = new ClassMock(
                new[] {new object(), new object()},
                true,
                i,
                new object());
        }
    }
}

internal sealed class ClassMock
{
    public readonly object[] Array;
    public readonly bool Bool;
    public readonly int Int;
    public readonly object Obj;

    public ClassMock(object[] array, bool b, int i, object obj)
    {
        Array = array;
        Bool = b;
        Int = i;
        Obj = obj;
    }
}

BenchmarkDotNet=v0.13.5, OS=Windows 11 (10.0.22621.1702/22H2/2022Update/SunValley2)
AMD Ryzen 7 5800H with Radeon Graphics, 1 CPU, 16 logical and 8 physical cores
.NET SDK=7.0.203
  [Host]   : .NET 7.0.5 (7.0.523.17405), X64 RyuJIT AVX2
  .NET 7.0 : .NET 7.0.5 (7.0.523.17405), X64 RyuJIT AVX2

Job=.NET 7.0  Runtime=.NET 7.0  

Method	Mean	Error	StdDev	Ratio	RatioSD	Gen0	Allocated	Alloc Ratio
AddRange	35.61 ns	0.721 ns	0.802 ns	0.81	0.02	0.0114	96 B	0.55
AsEnumerable	27.76 ns	0.210 ns	0.164 ns	0.63	0.02	0.0114	96 B	0.55
Initializer	44.03 ns	0.880 ns	1.316 ns	1.00	0.00	0.0210	176 B	1.00
ToList	31.52 ns	0.442 ns	0.414 ns	0.71	0.02	0.0114	96 B	0.55
WithoutInitializer	44.39 ns	0.889 ns	0.988 ns	1.01	0.03	0.0210	176 B	1.00