== 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 | 3,403.4 ns |  28.52 ns |  26.67 ns
|       Index |   478.0 ns |   6.93 ns |   6.48 ns
|       First | 6,160.0 ns |  57.66 ns |  53.93 ns
| First_Index |   485.7 ns |   5.81 ns |   5.15 ns
|        Last | 6,034.3 ns |  20.34 ns |  16.98 ns
|  Last_Index |   408.3 ns |   2.54 ns |   2.38 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 int ElementAt()
{
    int result = default;

    for (var i = 0; i < LoopSize; i++)
    {
        result = data.ElementAt(i);
    }

    return result;
}

[Benchmark]
public int Index()
{
    int result = default;

    for (var i = 0; i < LoopSize; i++)
    {
        result = data[i];
    }

    return result;
}

[Benchmark]
public int First()
{
    int result = default;

    for (var i = 0; i < LoopSize; i++)
    {
        result = data.First();
    }

    return result;
}

[Benchmark]
public int First_Index()
{
    int result = default;

    for (var i = 0; i < LoopSize; i++)
    {
        result = data[0];
    }

    return result;
}

[Benchmark]
public int Last()
{
    int result = default;

    for (var i = 0; i < LoopSize; i++)
    {
        result = data.Last();
    }

    return result;
}

[Benchmark]
public int Last_Index()
{
    int result = default;

    for (var i = 0; i < LoopSize; i++)
    {
        result = data[data.Count - 1];
    }

    return result;
}
----

Hardware configuration:
----
BenchmarkDotNet=v0.13.5, OS=Windows 10 (10.0.19045.4412/22H2/2022Update)
11th Gen Intel Core i7-11850H 2.50GHz, 1 CPU, 16 logical and 8 physical cores
.NET SDK=8.0.301
  [Host]   : .NET 8.0.6 (8.0.624.26715), X64 RyuJIT AVX2
  .NET 8.0 : .NET 8.0.6 (8.0.624.26715), X64 RyuJIT AVX2
----