C# Enumの文字列変換は重い

EnumをToStringすると激重なので、事前にswitch文やarrayで文字列を定義しておくと、パフォーマンスを上げることができる

コード

[RankColumn]
public class EnumTest
{
	[Params(Weapon.WeaponType.A)]
	public Weapon.WeaponType weaponType;

	[Benchmark]
	public string Case1()
	{
		return weaponType.GetNameSwitch();
	}

	[Benchmark]
	public string Case2()
	{
		return weaponType.GetNameArray();
	}

	[Benchmark]
	public string Case3()
	{
		return weaponType.GetNameToString();
	}
}

public static class Weapon
{
	public enum WeaponType
	{
		A,
		B,
		C,
	}

	private static string[] weaponTypeArray = {
		"A",
		"B",
		"C",
	};

	public static string GetNameSwitch(this WeaponType type)
	{
		switch (type)
		{
			case WeaponType.A: return "A";
			case WeaponType.B: return "B";
			case WeaponType.C: return "C";
		}
		throw new NotImplementedException();
	}

	public static string GetNameArray(this WeaponType type)
	{
		return weaponTypeArray[(int)type];
	}

	public static string GetNameToString(this WeaponType type)
	{
		return type.ToString();
	}
}

結果

//BenchmarkDotNet=v0.12.0, OS=Windows 10.0.18362
//Intel Core i5-9600K CPU 3.70GHz(Coffee Lake), 1 CPU, 6 logical and 6 physical cores
// [Host]     : .NET Framework 4.8 (4.8.4121.0), X64 RyuJIT
//  DefaultJob : .NET Framework 4.8 (4.8.4121.0), X64 RyuJIT

//| Method | weaponType |        Mean |     Error |    StdDev | Rank |
//|------- |----------- |------------:|----------:|----------:|-----:|
//|  Case1 |          A |   1.2287 ns | 0.0263 ns | 0.0246 ns |    2 |
//|  Case2 |          A |   0.0523 ns | 0.0123 ns | 0.0115 ns |    1 |
//|  Case3 |          A | 282.2946 ns | 1.4594 ns | 1.3652 ns |    3 |