TestYield.cs

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

public class TestYield : MonoBehaviour 
{
    public void Start() {
        TestAdd();
        TestOperator();
    }

    public IntList GetIntList()
    {
        //return new IntList();
        return new IntListWithYield();
        //return new IntListExpandPrint();
    }

    public void TestAdd()
    {
        IntList list = GetIntList();
        list.Add(3);
        list.Add(5);
        list.Add(7);

        list.Print();
    }

    public void TestAdd2()
    {
        IntList list = GetIntList();
        for (int i = 0; i < 100; i++)
        {
            list.Add(i);
        }
        list.Print();
    }

    public void TestOperator()
    {
        IntList list = GetIntList();
        list.Add(3);
        list.Add(5);
        list.Add(7);

        list.Print();

        list[0] = 1;

        list.Print();
    }

    public class IntList : IEnumerable {
        static readonly int INITIAL_SLOTS = 10;
        protected int[] values = new int[INITIAL_SLOTS];
        protected int next = 0;

        public void Add(int value) 
        {
            values[next++] = value;
            if (next >= values.Length) {
                Expand();
            }
        }
        public int Get(int index) 
        {
            if (index >= next || index < 0) throw new System.ArgumentException();
            return values[index];
        }

        public void Set(int index, int value) {
            if (index > next || index < 0) throw new System.ArgumentException();
            values[index] = value;
        }

        public int this[int index] 
        {
            get { return Get(index); }
            set { Set(index, value);  }
        }

        private void Expand() 
        {
            int[] newValues = new int[values.Length * 2];
            for (int i = 0; i < values.Length; i++)
            {
                newValues[i] = values[i];
            }
            values = newValues;
        }
        public int Count { get { return next; } }

        public virtual IEnumerator GetEnumerator()
        {
            return new IntListEnum(this);
        }

        public virtual void Print()
        {
            foreach (var i in this)
            {
                Debug.Log(i);
            }
        
        }

        public class IntListEnum : IEnumerator
        {
            int next = -1;
            IntList list;

            public IntListEnum(IntList list) 
            {
                this.list = list;
            }
            object IEnumerator.Current { 
                get {
                    try
                    {
                        return list.values[next];
                    }
                    catch (System.ArgumentOutOfRangeException)
                    {
                        return new System.InvalidOperationException();
                    }
                } 
            }

            public bool MoveNext()
            {
                next++;
                if (next >= list.Count)
                {
                    return false;
                }
                else 
                {
                    return true;
                }
            }

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

    public class IntListWithYield : IntList
    {
        public override IEnumerator GetEnumerator()
        {
            yield return StartCoroutine(GetEnumeratorImpl());
            
        }

        private object StartCoroutine(IEnumerator e)
        {
            while (e.MoveNext())
                return e.Current;
            return null;
        }

        private IEnumerator GetEnumeratorImpl()
        {
            for (int i = 0; i < next; i++)
            {
                yield return values[i];
            }
        }


    }

    public class IntListExpandPrint : IntList
    {
        public override void Print()
        {
            IEnumerator enumerator = GetEnumerator();
            while (enumerator.MoveNext())
            {
                object curr = enumerator.Current;
                Debug.Log(curr);
            }
        }
    }
}