Introduction

As you may know, in order to be able to iterate on a collection in C# with the foreach loop the collection must expose a public method GetEnumerator() which doesn’t exist on IEnumerator and IAsyncEnumerator interfaces. C## 9 allows to create an extension method to allow foreach loops on those interfaces. Let’s see in this article how to proceed.

Implement a GetEnumerator extension

It’s quite easy you just have to create an extension method like this:

public static class Extensions
{
        public static IEnumerator<T> GetEnumerator<T>(this IEnumerator<T> enumerator) => enumerator;
}

Make sure that extension method is accessible everywhere in your program, and you’ll be able to apply it anywhere.

Usually when you try to iterate with a foreach loop on a collection typed IEnumerator or IAsyncEnumerator you’ll get this message:

Error CS1579 foreach statement cannot operate on variables of type ‘IEnumerator’ // because ‘IEnumerator’ does not contain a public instance or extension definition for ‘GetEnumerator’

With C## 9 and the previous extension (together only) shown above only we can make it work, example:

using System;
using System.Collections.Generic;

namespace CSharp9Demo
{
    public static class Extensions
    {
        public static IEnumerator<T> GetEnumerator<T>(this IEnumerator<T> enumerator) => enumerator;
    }

    class Program
    {
        static void Main()
        {
            IEnumerator<string> countryEnumerator = (IEnumerator<string>)new List<string> { "France", "Canada", "Japan" };

            // Before C## 9: Error CS1579  foreach statement cannot operate on variables of type 'IEnumerator<string>' 
            // because 'IEnumerator<string>' does not contain a public instance or extension definition for 'GetEnumerator'
            foreach (var country in countryEnumerator)
            {
                Console.WriteLine($"{country} is a beautiful country");
            }
        }
    }
}

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