关于网上讨论Foreach循环会不会产生GC的问题，不如自己实验一番，我用的Unity版本是2021.3.23f1c1版本。

测试代码如下：

using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Profiling;

namespace Test
{
    public class MyGCTest : MonoBehaviour
    {
        Dictionary<int, float> dic1 = new Dictionary<int, float>()
        {
            { 0, 0.2f },
            { 100, 100.0f }
        };

        Dictionary<int, int> dic2 = new Dictionary<int, int>()
        {
            { 0, 0 },
            { 100, 100 }
        };

        Dictionary<int, string> dic3 = new Dictionary<int, string>()
        {
            { 0, "0.2f" },
            { 100, "100.0f" }
        };

        Dictionary<string, int> dic4 = new Dictionary<string, int>()
        {
            { "0", 0 },
            { "100", 100 }
        };

        List<int> list1 = new List<int>() { 0, 1, 0 };
        List<bool> list4 = new List<bool>() { false, true, false };
        List<char> list5 = new List<char>() { 'f', 'a', 'b' };
        List<string> list3 = new List<string>() { "6", "2", "3" };
        List<TestClass> list2 = new List<TestClass>() { new TestClass("6"), new TestClass("2"), new TestClass("3") };
        List<TestClass2> list6 = new List<TestClass2>() { new TestClass2(6), new TestClass2(2), new TestClass2(3) };
        int[] arr1 = new int[3] { 0, 1, 0 };
        bool[] arr2 = new bool[3] { false, true, false };
        char[] arr3 = new char[3] { 'f', 'a', 'b' };
        string[] arr4 = new string[3] { "6", "2", "3" };
        TestClass[] arr5 = new TestClass[3] { new TestClass("6"), new TestClass("2"), new TestClass("3") };

        void Update()
        {
            //----------------------字典-----------------
            Profiler.BeginSample("ForeachGC.dic1");
            foreach (var x in dic1)
            {
            }

            Profiler.EndSample();

            Profiler.BeginSample("ForeachGC.dic2");
            foreach (var x in dic2)
            {
            }

            Profiler.EndSample();

            Profiler.BeginSample("ForeachGC.dic3");
            foreach (var x in dic3)
            {
            }

            Profiler.EndSample();

            Profiler.BeginSample("ForeachGC.dic4");
            foreach (var x in dic4)
            {
            }

            Profiler.EndSample();

            Profiler.BeginSample("ForeachGC.dic1第二次调用");
            foreach (var x in dic1)
            {
            }

            Profiler.EndSample();

            Profiler.BeginSample("ForeachGC.dic1.Values");
            foreach (var x in dic1.Values)
            {
            }

            Profiler.EndSample();
            //----------------------列表-----------------
            Profiler.BeginSample("ForeachGC.list1");
            foreach (var x in list1)
            {
            }

            Profiler.EndSample();
            
            
            Profiler.BeginSample("ForeachGC.list2");
            foreach (var x in list2)
            {
            }

            Profiler.EndSample();

            Profiler.BeginSample("ForeachGC.list3");
            foreach (var x in list3)
            {
            }

            Profiler.EndSample();

            Profiler.BeginSample("ForeachGC.list4");
            foreach (var x in list4)
            {
            }

            Profiler.EndSample();
            
            Profiler.BeginSample("ForeachGC.list5");
            foreach (var x in list5)
            {
            }

            Profiler.EndSample();
            
            Profiler.BeginSample("ForeachGC.list6");
            foreach (var x in list6)
            {
            }

            Profiler.EndSample();
            //----------------------数组-----------------
            Profiler.BeginSample("ForeachGC.arr1");
            foreach (var x in arr1)
            {
            }

            Profiler.EndSample();

            Profiler.BeginSample("ForeachGC.arr2");
            foreach (var x in arr2)
            {
            }

            Profiler.EndSample();

            Profiler.BeginSample("ForeachGC.arr3");
            foreach (var x in arr3)
            {
            }

            Profiler.EndSample();

            Profiler.BeginSample("ForeachGC.arr4");
            foreach (var x in arr4)
            {
            }

            Profiler.EndSample();

            Profiler.BeginSample("ForeachGC.arr5");
            foreach (var x in arr5)
            {
            }

            Profiler.EndSample();
        }
    }

    public class TestClass
    {
        private string sd2;

        public TestClass(string sd)
        {
            sd2 = sd;
        }
    }

    public class TestClass2
    {
        private int sd2;

        public TestClass2(int sd)
        {
            sd2 = sd;
        }
    }
}

第一帧产生GC；

第二帧不产生GC

后面都不产生GC

结论如下：

1. 不同键值字典对的字典第一帧会产生48B的GC，键值对相同的字典只会产生一次GC；
2. 遍历字典的Value会产生120BGC
3. 遍历数组均不会产生GC
4. 遍历List时，值类型会在首帧产生48BGC，引用类型不会产生GC