Unity C# for和foreach效率比較

先說測試結果：
for比foreach快，for循環不額外定義length彷佛更快

測試代碼：

using UnityEngine;
using UnityEditor;
using System.Diagnostics;

/// <summary>
/// 執行時間測試
/// ZhangYu 2019-04-13
/// </summary>
public class TimeTest : MonoBehaviour {

    private static Stopwatch watch;

    private void Start() {
        Execute();
    }

    [MenuItem("CONTEXT/TimeTest/執行")]
    private static void Execute() {
        watch = new Stopwatch();

        // 數據長度
        int total = 100000000;
        int[] array = new int[total];
        for (int i = 0; i < total; i++) {
            array[i] = i + 1;
        }

        // Foreach
        watch.Reset();
        watch.Start();
        ForeachTest(array);
        watch.Stop();
        string msgForeach = string.Format("Foreach: {0}s", watch.Elapsed);

        // For1
        watch.Reset();
        watch.Start();
        ForTest1(array);
        watch.Stop();
        string msgFor1 = string.Format("For1: {0}s", watch.Elapsed);

        // For2
        watch.Reset();
        watch.Start();
        ForTest2(array);
        watch.Stop();
        string msgFor2 = string.Format("For2: {0}s", watch.Elapsed);

        print(msgForeach);
        print(msgFor1);
        print(msgFor2);
    }

    // (1)0.7167410s
    // (2)0.7127794s
    // (3)0.7215614s
    // (4)0.7183622s
    // (5)0.7190012s
    public static void ForeachTest(int[] array) {
        foreach (int item in array) {

        }
    }

    // (1)0.5252327s
    // (2)0.5546530s
    // (3)0.5545011s
    // (4)0.5576123s
    // (5)0.5543154s
    public static void ForTest1(int[] array) {
        for (int i = 0; i < array.Length; i++) {

        }
    }

    // (1)0.5314386s
    // (2)0.5835369s
    // (3)0.5908804s
    // (4)0.5880162s
    // (5)0.5835442s
    public static void ForTest2(int[] array) {
        int length = array.Length;
        for (int i = 0; i < length; i++) {

        }
    }
}

測試結果：
排除運行環境的偏差，for循環和foreach循環在數十次的測試結果中，for更快一點，For2方法優化了一下length的取值，彷佛定義了length比直接使用array.Length更慢了一點兒，仍是直接使用array.length吧。