c#：自定義泛型棧實現 IEnumerable IEnumerator

只有繼承 IEnumerable IEnumerator 的類才能使用foreach。
點進去看可以看到IEnumerable的接口定義的是

public interface IEnumerable<out T> : IEnumerable

繼承了IEnumerable
IEnumerable只有一個方法，返回可循環訪問集合的枚舉數
IEnumerator GetEnumerator() ;

demo
IStack.cs

internal interface IStack<T> : IEnumerable<T>, IEnumerator<T>
{
    void Push(T value);

    void Pop();

    T Peek();

    void Empty();

    bool IfEmpty();

    int Count();
}

MyStack.cs 前一半是定義的棧結構

internal class MyStack<T> : IStack<T>
{
    private List<T> datas;
    public int index;
    public int eumerableIndex;

    public MyStack()
    {
        datas = new List<T>();
        index = -1;
        eumerableIndex = -1;
    }

    public int Count()
    {
        return index + 1;
    }

    public void Empty()
    {
        datas.Clear();
        index = -1;
    }

    public bool IfEmpty()
    {
        return (datas.Count == 0);
    }

    public T Peek()
    {
        T top;
        if (index > 0)
        {
            top = datas[datas.Count - 1];
        }
        else
        {
            top = default(T);
            Console.WriteLine("Empty stack, Peek failed");
        }
        return top;
    }

    public void Push(T value)
    {
        datas.Add(value);
        index++;
    }

    public void Pop()
    {
        if (index >= 0)
        {
            datas.RemoveAt(index);
            index--;
            Console.WriteLine("Pop");
        }
        else
        {
            Console.WriteLine("Empty Stack, Pop failed");
        }
    }

    public override String ToString()
    {
        StringBuilder resultBuilder = new StringBuilder();
        if (index < 0)
        {
            resultBuilder.Append("Empty");
        }
        else
        {
            for (int i = 0; i < index + 1; i++)
            {
                resultBuilder.Append(" ");
                resultBuilder.Append(datas[i].ToString());
            }
        }
        return resultBuilder.ToString();
    }

    public T Current
    {
        get
        {
            return datas[eumerableIndex];
        }
    }

    public bool MoveNext()
    {
        return ++eumerableIndex < datas.Count;
    }

    object IEnumerator.Current
    {
        get
        {
            return Current;
        }
    }

    public void Dispose()
    {
        eumerableIndex = -1;
    }

    public IEnumerator<T> GetEnumerator()
    {
        return this;
    }

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

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

接下來聲明的MyStack就可以使用foreach方法了

MyStack<int> myStack = new MyStack<int>();
myStack.Push(1);
myStack.Push(2);
foreach (var val in myStack)
{
    Console.WriteLine(val);
}