IReadOnlyList ForEach vs Array ForLoop - allocation

IReadOnlyList Enumerator allocation

Result

``` ini

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19042
Intel Xeon CPU E5-1650 v4 3.60GHz, 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=5.0.100-rc.2.20479.15
  [Host]     : .NET Core 3.1.9 (CoreCLR 4.700.20.47201, CoreFX 4.700.20.47203), X64 RyuJIT
  DefaultJob : .NET Core 3.1.9 (CoreCLR 4.700.20.47201, CoreFX 4.700.20.47203), X64 RyuJIT


```
|                    Method |     Mean |    Error |   StdDev |  Gen 0 | Gen 1 | Gen 2 | Allocated |
|-------------------------- |---------:|---------:|---------:|-------:|------:|------:|----------:|
| MergeIReadonlyListForloop | 90.64 ns | 1.894 ns | 4.501 ns | 0.0285 |     - |     - |     224 B |
| MergeIReadonlyListForEach | 87.03 ns | 1.796 ns | 3.145 ns | 0.0325 |     - |     - |     256 B |
|         MergeArrayForLoop | 48.62 ns | 1.021 ns | 1.560 ns | 0.0286 |     - |     - |     224 B |




Code used


using BenchmarkDotNet.Attributes;
using System.Collections.Generic;

namespace Benchmark_ToListCall
{
    [MemoryDiagnoser]
    public class CollectionBenchmarks2
    {
        public class WebComponent
        {
            public int Id { set; get; }
            public string Name { set; get; }

            public int Position { set; get; }

        }

        private int[] positions;
        private WebComponent[] components = new WebComponent[5];
        [GlobalSetup]
        public void GlobalSetup()
        {
            components[0] = new WebComponent { Id = 1, Name = "A", Position = 1 };
            components[1] = new WebComponent { Id = 2, Name = "B", Position = 2 };
            components[2] = new WebComponent { Id = 3, Name = "C", Position = 3 };
            components[3] = new WebComponent { Id = 4, Name = "D", Position = 4 };
            components[4] = new WebComponent { Id = 5, Name = "E", Position = 5 };

            positions = new int[] { 2, 4, 6, 8, 10 };
        }       
        

        [Benchmark]
        public WebComponent[] MergeIReadonlyListForloop()
        {
            return this.MergeIReadonlyListForloop(this.components, this.positions);
        }
        [Benchmark]
        public WebComponent[] MergeIReadonlyListForEach()
        {
            return this.MergeIReadonlyListForEach(this.components, this.positions);
        }
        [Benchmark]
        public WebComponent[] MergeArrayForLoop()
        {
            return this.MergeArrayForLoop(this.components, this.positions);
        }

        private WebComponent[] MergeIReadonlyListForloop(IReadOnlyList<WebComponent> components, int[] positions)
        {
            var combinedComponents = new WebComponent[components.Count];
            for (int i = 0; i < components.Count; i++)
            {
                var webComponent = new WebComponent
                {
                    Name = components[i].Name,
                    Position = positions[i]
                };

                combinedComponents[i] = webComponent;
            }

            return combinedComponents;
        }

        private WebComponent[] MergeIReadonlyListForEach(IReadOnlyList<WebComponent> components, int[] positions)
        {
            var combinedComponents = new WebComponent[components.Count];

            int i = 0;
            foreach(var item in components)
            {
                var webComponent = new WebComponent
                {
                    Name = item.Name,
                    Position = positions[i]
                };
                combinedComponents[i] = webComponent;
                i++;
            }


            return combinedComponents;
        }
        private WebComponent[] MergeArrayForLoop(WebComponent[] components, int[] positions)
        {
            var combinedComponents = new WebComponent[components.Length];
            for (int i = 0; i < components.Length; i++)
            {
                var webComponent = new WebComponent
                {
                    Name = components[i].Name,
                    Position = positions[i]
                };

                combinedComponents[i] = webComponent;
            }

            return combinedComponents;
        }        
    }

}