UnityのSwitchとDictionaryのパフォーマンス計測

気になって調べてみました。
Enumをキーにした走査のパフォーマンス計測です、詳しくはソースコードを確認してみてください。
1000回まではDictionaryが優位な理由が理解できませんでした。
実機検証だとまた違ってくるのかな。

追記（2018/11/15）

IEqualityComparerを使用したパターンを追加しました。

環境情報

• Unity2018.2
• C# 6.0

計測結果（ms）

回数	Switch	Dictionary	Dictionary with EqualityComparer
1000	0.6702	0.5385	0.2337
10000	0.4978	1.0851	0.8194
100000	4.4215	10.186	7.2272
1000000	41.3294	101.584	71.413

ソースコード

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using UnityEngine;
using Debug = UnityEngine.Debug;
using Random = System.Random;

namespace BenchMarks
{
    public class SwitchVsDictionary : MonoBehaviour
    {
        private Random _random = new Random();
        private String _logText = "";

        private void Start()
        {
            _logText += "|回数|Switch|Dictionary|Dictionary with EqualityComparer|\n";
            _logText += "|---|--:|--:|--:|\n";

            _logText += "|1000";
            Benchmark(1000);

            _logText += "|10000";
            Benchmark(10000);

            _logText += "|100000";
            Benchmark(100000);

            _logText += "|1000000";
            Benchmark(1000000);

            Debug.Log(_logText);
        }

        private void Benchmark (int benchmarkCount)
        {
            var randomNumbers = new List<Number>();
            for (var i = 0; i < benchmarkCount; i++)
            {
                var randomNumber = Enum.GetValues(typeof(Number))
                    .Cast<Number>()
                    .OrderBy(c => _random.Next())
                    .FirstOrDefault();
                randomNumbers.Add(randomNumber);
            }

            var stopWatch = new Stopwatch();
            stopWatch.Start();

            foreach (var number in randomNumbers)
            {
                GetBySwitch(number);
            }

            stopWatch.Stop();

            _logText += $"{stopWatch.Elapsed.TotalMilliseconds}|";

            stopWatch.Restart();

            foreach (var number in randomNumbers)
            {
                GetByDictionary(number);
            }

            stopWatch.Stop();

            _logText += $"{stopWatch.Elapsed.TotalMilliseconds}|";

            stopWatch.Restart();

            foreach (var number in randomNumbers)
            {
                GetByDictionaryWithEqualityComparer(number);
            }

            stopWatch.Stop();

            _logText += $"{stopWatch.Elapsed.TotalMilliseconds}|\n";
        }

        // Switch
        enum Number
        {
            One,
            Two,
            Three,
            Four,
            Five,
            Six,
            Seven,
            Eight,
            Nine,
            Ten
        }

        private int GetBySwitch(Number number)
        {
            switch (number)
            {
                case Number.One:
                    return 1;
                case Number.Two:
                    return 2;
                case Number.Three:
                    return 3;
                case Number.Four:
                    return 4;
                case Number.Five:
                    return 5;
                case Number.Six:
                    return 6;
                case Number.Seven:
                    return 7;
                case Number.Eight:
                    return 8;
                case Number.Nine:
                    return 9;
                case Number.Ten:
                    return 10;
                default:
                    return default(int);
            }
        }

        // Dictionary
        private readonly Dictionary<Number, int> _numberTable = new Dictionary<Number, int>
        {
            { Number.One,    1 },
            { Number.Two,    2 },
            { Number.Three,  3 },
            { Number.Four,   4 },
            { Number.Five,   5 },
            { Number.Six,    6 },
            { Number.Seven,  7 },
            { Number.Eight,  8 },
            { Number.Nine,   9 },
            { Number.Ten,   10 }
        };

        private int GetByDictionary(Number number)
        {
            return _numberTable[number];
        }

        // Dictionary with EqualityComparer
        private class NumberComparer : IEqualityComparer<Number>
        {
            public bool Equals(Number x, Number y)
            {
                return x == y;
            }

            public int GetHashCode(Number obj)
            {
                return (int)obj;
            }
        }

        private readonly Dictionary<Number, int> _numberTableWithEqualityComparer = new Dictionary<Number, int>(new NumberComparer())
        {
            { Number.One,    1 },
            { Number.Two,    2 },
            { Number.Three,  3 },
            { Number.Four,   4 },
            { Number.Five,   5 },
            { Number.Six,    6 },
            { Number.Seven,  7 },
            { Number.Eight,  8 },
            { Number.Nine,   9 },
            { Number.Ten,   10 }
        };

        private int GetByDictionaryWithEqualityComparer(Number number)
        {
            return _numberTableWithEqualityComparer[number];
        }
    }
}