Benchmarking DateTime.ToString("...")

Looking to eek-out as much perf as I can from some code (C#) at work, and looking at all the .ToString() manipulations in the code and I came across the following:

	public static class DateExtensions
	{
	public static string ToSqlDateTime(this System.DateTime dateTime) => dateTime.ToString("yyyy-MM-dd");
	}

view raw DateExtensions.cs hosted with ❤ by GitHub

How can I quickly workout if I want to do something around this?

BenchmarkDotNet to the rescue, and this library really does make benchmarking easy (and fun!). I created an overload of the extension method which internally uses a cache to avoid the repeative ToString() calls:

	public static class DateExtensions
	{
	private static readonly ConcurrentDictionary<System.DateTime, string> Cached = new ConcurrentDictionary<System.DateTime, string>();
	public static string ToSqlDateTime(this System.DateTime dateTime) => dateTime.ToString("yyyy-MM-dd");
	public static string ToSqlDateTimeCached(this System.DateTime dateTime)
	{
	if (Cached.TryGetValue(dateTime, out var value))
	return value;
	value = dateTime.ToSqlDateTime();
	Cached.AddOrUpdate(dateTime, _ => value, (_, _) => value);
	return value;
	}
	}

view raw DateExtensions_Benchmark.cs hosted with ❤ by GitHub

Only small issue was wanting to test a Static methods, and this only involved creating a wrapper class with annotated methods(calling the static implementations), also preloaded the internal cache:

	public class Instance
	{
	private readonly System.DateTime _date;
	public Instance()
	{
	_date = new System.DateTime(2022, 08, 10);
	var date = new System.DateTime(2021, 1, 1);
	for (var i = 0; i < 100; i++)
	{
	date = date.AddDays(i);
	date.ToSqlDateTimeCached();
	}
	}
	[Benchmark]
	public string CallStaticMethod_ToSqlDateTime() => _date.ToSqlDateTime();
	[Benchmark]
	public string CallStaticMethod_ToSqlDateTimeCached() => _date.ToSqlDateTimeCached();
	}

view raw Benchmark_Instance.cs hosted with ❤ by GitHub

Results below, make-of-it what you will...