C#如何为嵌套类实现IEnumerable

using System;
using System.Collections;

public class OuterClass
{
    private int[] data;

    public OuterClass()
    {
        data = new int[] { 1, 2, 3, 4, 5 };
    }

    public IEnumerator GetEnumerator()
    {
        return new NestedClassEnumerator(data);
    }

    private class NestedClassEnumerator : IEnumerator
    {
        private int[] data;
        private int position = -1;

        public NestedClassEnumerator(int[] data)
        {
            this.data = data;
        }

        public object Current
        {
            get
            {
                if (position == -1 || position >= data.Length)
                    throw new InvalidOperationException();
                return data[position];
            }
        }

        public bool MoveNext()
        {
            position++;
            return (position < data.Length);
        }

        public void Reset()
        {
            position = -1;
        }
    }
}

public class Program
{
    public static void Main()
    {
        OuterClass outer = new OuterClass();
        foreach (int num in outer)
        {
            Console.WriteLine(num);
        }
    }
}