== Resources

=== Documentation

* https://learn.microsoft.com/en-us/dotnet/api/system.collections.ilist.item[IList.Item[Int32\]]
* https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.ilist-1.item[IList<T>.Item[Int32\]]
* https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.ireadonlylist-1.item[IReadonlyList<T>.Item[Int32\]]

=== Benchmarks

[options="header"]
|===
| Method | Runtime | Mean | Standard Deviation
| ElementAt | .NET 7.0 | 15,193.1 ns |  233.47 ns
| Index | .NET 7.0 | 9,465.6 ns | 148.16 ns
| First | .NET 7.0 | 7,790.2 ns | 165.70 ns
| First_Index | .NET 7.0 | 398.5 ns | 5.36 ns
| Last | .NET 7.0 | 7,398.2 ns |  152.48 ns
| Last_Index | .NET 7.0 | 347.3 ns | 5.47 ns
| ElementAt | .NET Framework 4.6.2 | 12,205.7 ns | 298.49 ns
| Index | .NET Framework 4.6.2 | 8,917.8 ns | 51.55 ns
| First | .NET Framework 4.6.2 | 5,109.1 ns | 100.13 ns
| First_Index | .NET Framework 4.6.2 | 566.0 ns | 6.56 ns
| Last | .NET Framework 4.6.2 | 5,052.7 ns | 76.02 ns
| Last_Index | .NET Framework 4.6.2 | 680.7 ns | 9.56 ns
|===

==== Glossary

* https://en.wikipedia.org/wiki/Arithmetic_mean[Mean]
* https://en.wikipedia.org/wiki/Standard_deviation[Standard Deviation]

The results were generated by running the following snippet with https://github.com/dotnet/BenchmarkDotNet[BenchmarkDotNet]:

[source,csharp]
----
private List<byte> data;
private Random random;

[Params(1_000_000)]
public int SampleSize;

[Params(1_000)]
public int LoopSize;

[GlobalSetup]
public void Setup()
{
    random = new Random(42);
    var bytes = new byte[SampleSize];
    random.NextBytes(bytes);
    data = bytes.ToList();
}

[Benchmark]
public void ElementAt()
{
    for (int i = 0; i < LoopSize; i++)
    {
        var index = random.Next(0, SampleSize);
        _ = data.ElementAt(index);
    }
}

[Benchmark]
public void Index()
{
    for (int i = 0; i < LoopSize; i++)
    {
        var index = random.Next(0, SampleSize);
        _ = data[index];
    }
}

[Benchmark]
public void First()
{
    for (int i = 0; i < LoopSize; i++)
    {
        _ = data.First();
    }
}

[Benchmark]
public void First_Index()
{
    for (int i = 0; i < LoopSize; i++)
    {
        _ = data[0];
    }
}

[Benchmark]
public void Last()
{
    for (int i = 0; i < LoopSize; i++)
    {
        _ = data.Last();
    }
}

[Benchmark]
public void Last_Index()
{
    for (int i = 0; i < LoopSize; i++)
    {
        _ = data[data.Count - 1];
    }
}
----

Hardware configuration:
----
BenchmarkDotNet=v0.13.5, OS=Windows 10 (10.0.19045.2846/22H2/2022Update)
11th Gen Intel Core i7-11850H 2.50GHz, 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
  .NET Framework 4.6.2 : .NET Framework 4.8.1 (4.8.9139.0), X64 RyuJIT VectorSize=256
----