Having trouble understanding IEnumerator

Question

I'm currently learing C# for the purpose of effectivly usingRazor and Umbraco, I have a little bit of background in PHP and a reasonable knowledge in JavaScript.

I came across the IEnumerator interface and have had difficulty getting my head around it. I've setup a code snippet below to demonstrate looping through an array with foreach:

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace cardEnum
{
    class suitsEnumerator
    {
        private static string[] suits = { "Hearts", "Spades", "Diamonds", "Clubs" };
        public void showAll()
        {
            foreach(string x in suits){
                System.Console.WriteLine(x);
            }
        }
    }
    class run
    {
        static void Main()
        {
            Console.WriteLine("The suits are:");
            var suits = new suitsEnumerator();
            suits.showAll();
            Console.ReadKey();
        }
    }
}

Can someone explain why I would even need to use IEnumerator when I can quite easily loop through the array otherwise. I KNOW this is such a simple question, I just cant think of an reason to use IEnumerable.

Any help at all would be greatly appreciated, thanks!

Answer 1

This is how the enumerator pattern could be implemented in your example. I hope this clarifies a few things, in particular, the relationship between IEnumerable and IEnumerator:

namespace cardEnum {
    // simple manual enumerator
    class SuitsEnumerator : IEnumerator {
        private int pos = -1;
        private static string[] suits = { "Hearts", "Spades", "Diamonds", "Clubs" };

        public object Current {
            get { return suits[pos]; }
        }

        public bool MoveNext() {
            pos++;
            return (pos < suits.Length);
        }

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

    class Suits : IEnumerable {
        public IEnumerator GetEnumerator() {
            return new SuitsEnumerator();
        }
    }

    class run {
        static void Main() {
            Console.WriteLine("The suits are:");
            var suits = new Suits();
            foreach (var suit in suits) {
                Console.WriteLine(suit);
            }
            Console.ReadKey();
        }
    }
}

Of course, this is a contrived example to aid understanding. Since string[] already implements IEnumerable, there's no reason to reinvent the wheel.

---

Since C# supports the yields keyword, creating an Enumerator got a little easier recently:

namespace cardEnum {
    // no explicit SuitsEnumerator required
    class Suits : IEnumerable {
        public IEnumerator GetEnumerator() {
            yield return "Hearts";
            yield return "Spades";
            yield return "Diamonds";
            yield return "Clubs";
        }
    }

    class run {
        static void Main() {
            Console.WriteLine("The suits are:");
            var suits = new Suits();
            foreach (var suit in suits) {
                Console.WriteLine(suit);
            }
            Console.ReadKey();
        }
    }
}