Performance comparison between int and enum.

EnumAsMetricBenchmark.cs

using System;
using UnityEngine;
using UnityEngine.UI;

/******** Result *********
* TestIntConversion: .0032730
* TestEnumConversion: .0029910
* TestIntOp: .0027300
* TestEnumOp: .0030000 <- always lose :(
* TestIntToString: .3037160
* TestEnumToString: 2.7711720
* TestEnumToStringCustom: .3533840
* TestEnumToStringCustomInline: .3253510
**************************/

public enum Meter
{
}

public class EnumAsMetricBenchmark : MonoBehaviour
{
    const int _iteration = 100000;

    public Text Text;

    public void Test()
    {
        _text = Text;
        _text.text = "";
        Test(TestIntConversion);
        Test(TestEnumConversion);
        Test(TestIntOp);
        Test(TestEnumOp);
        Test(TestIntToString);
        Test(TestEnumToString);
        Test(TestEnumToStringCustom);
        Test(TestEnumToStringCustomInline);
    }

    static Text _text;

    static void TestIntConversion(int i)
    {
        var x = i;
        var y = (int) x;
    }

    static void TestEnumConversion(int i)
    {
        var x = default(Meter);
        var y = (int) x;
    }

    static void TestIntOp(int i, int j)
    {
        var a = i;
        var b = j;
        var c = a + b;
    }

    static void TestEnumOp(int i, int j)
    {
        var a = (Meter) i;
        var b = j;
        var c = a + b;
    }

    static void TestIntToString(int i)
    {
        i.ToString();
    }

    static void TestEnumToString(int i)
    {
        var a = (Meter) i;
        a.ToString();
    }

    static void TestEnumToStringCustom(int i)
    {
        var a = (Meter) i;
        a.ToStr();
    }

    static void TestEnumToStringCustomInline(int i)
    {
        var a = (Meter) i;
        ((int) a).ToString();
    }

    static void Test(Action<int> func)
    {
        var startTime = DateTime.Now;
        for (var i = 0; i != _iteration; ++i)
            func(i);
        var doneTime = DateTime.Now;
        _text.text += func.Method.Name + ": " + (doneTime - startTime) + "\n";
    }

    static void Test(Action<int, int> func)
    {
        var startTime = DateTime.Now;
        for (var i = 0; i != _iteration; ++i)
            func(i, i / 3);
        var doneTime = DateTime.Now;
        _text.text += func.Method.Name + ": " + (doneTime - startTime) + "\n";
    }
}

public static class ExtensionMethods
{
    public static string ToStr(this Meter thiz)
        => ((int) thiz).ToString();
}