Goal: In C#, convert a string to lower case. e.g. "TEST STRING" becomes "test string"

baseline.cs

internal class Program
{
	private static void Main()
	{
		var s = "TEST STRING";
		var lower = s.ToLower();
		Debug.Assert(lower == "test string");
	}
}

HowWeReallyWriteForLoopsNow.cs

internal class Program
{
	private static void Main()
	{
		var s = "TEST STRING";
		var lower = s.Aggregate(string.Empty, (current, c) => current + char.ToLower(c));

		Debug.Assert(lower == "test string");
	}
}

MethodInfoMoreLikeTotallyWinningInfo.cs

internal class Program
{
	private static void Main()
	{
		var lowerMethod = typeof (string).GetMethods().First(m => m.Name == "ToLower");
		var lower = lowerMethod.Invoke("TEST STRING", null).ToString();
		Debug.Assert(lower == "test string");
	}
}

OldSchoolCool.cs

internal class Program
{
	private static void Main()
	{
		var s = "TEST STRING";
		var lower = string.Empty;
		for (var i = 0; i < s.Length; i++)
		{
			lower += char.ToLower(s[i]);
		}

		Debug.Assert(lower == "test string");
	}
}

SomeLINQ.cs

internal class Program
{
	private static void Main()
	{
		var s = "TEST STRING";
    		var lower = string.Empty;
		s.ToCharArray().ToList().ForEach(c => lower += c.ToString().ToLower());
		Debug.Assert(lower == "test string");
	}
}

SomeLINQwithExtensions.cs

	internal static class TheHelpers
	{
		public static char ToLower(this char c)
		{
			return char.ToLower(c);
		}

		public static IEnumerable<K> MapEach<T, K>(this IEnumerable<T> collection, Func<T, K> map)
		{
			return collection.Select(map);
		}

		public static string Join(this IEnumerable<char> chars, string seperator)
		{
			var en = chars.GetEnumerator();
			var sb = new StringBuilder();

			if (en.MoveNext())
				sb.Append(en.Current);

			while (en.MoveNext())
				sb.Append(seperator).Append(en.Current);

			return sb.ToString();
		}
	}

	internal class Program
	{
		private static void Main()
		{
			var s = "TEST STRING";
			var lower = s.MapEach(c => c.ToLower()).Join("");
			Debug.Assert(lower == "test string");
		}
	}

SuperDuperSafeVersionIfYouOnlyCareAboutEnglishWithNoFunnyBusiness.cs

	internal class Program
	{
		private static void Main()
		{
			var lower = "TEST STRING".Aggregate(string.Empty, (current, c) => current + (char)(c + 32) ).Replace('@', ' ');
			Debug.Assert(lower == "test string");
		}
	}

WeCanDoAbstractFactoriesToo.cs

internal class Program
{
	private static readonly IDictionary<Type, Func<object, string>> _poorExcuseForAbstractFactory = new Dictionary<Type, Func<object, string>>
	{
		{typeof(string), o => o.ToString().ToLower()}
	};

	private static void Main()
	{
		var s = "TEST STRING";
		var lower = _poorExcuseForAbstractFactory[s.GetType()](s);

		Debug.Assert(lower == "test string");
	}
}

YouCantRecurseWithoutCurse.cs

internal class Program
{
	private static void Main()
	{
		var s = "TEST STRING";
		var lower = RecursivelyLowercaseThatShizzle(s);
		Debug.Assert(lower == "test string");
	}

	public static string RecursivelyLowercaseThatShizzle(string s, int currentCharacterToProcess = 0)
	{
		if (currentCharacterToProcess < s.Length - 1)
		{
			return s.Substring(currentCharacterToProcess, 1).ToLower() + RecursivelyLowercaseThatShizzle(s, ++currentCharacterToProcess);
		}
		return s.Substring(currentCharacterToProcess, 1).ToLower();
	}
}

I feel like I need to add something that has an IAbstractHelloWorldFactoryFactory feel to it but I don't want to jump the shark.