ArrayList 註意點

1.

using System;
using System.Collections;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        var al = new ArrayList { 2, 3, true, "aa", true };
        //al.Clear();
        var count = al.Count;
        for (int i = 0; i < count; i++)
        {
            al.RemoveAt(0);
        }
        Console.WriteLine(al.Count);
    }
}

using System;
using System.Collections;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        var al = new ArrayList {"aa", "ab"};
        al.Remove(new string(new char[] {'a', 'b'}));
        foreach (var o in al)
        {
            Console.WriteLine(o);
        }
    }
}

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp3
{

    class Jjj : IEnumerable
    {
        private int _pos = -1;
        private int[] _ss = new int[] { 2, 3, 4, 5 };

        public int this[int index]
        {
            get => _ss[index];
            set => _ss[index] = value;
        }

        public int Count => _ss.Length;
        public IEnumerator GetEnumerator()
        {
            foreach (var i in _ss)
            {
                yield return i;
            }
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            var oj = new Jjj();
            var e = oj.GetEnumerator();
            while (e.MoveNext())
            {
                var cur = e.Current;
                Console.WriteLine(cur);
            }
            e.Reset();
            while (e.MoveNext())
            {
                var cur = e.Current;
                Console.WriteLine(cur);
            }
            foreach (var x in oj)
            {
                Console.WriteLine(x);
            }
        }
    }
}