Introducing C# 9: Extension GetEnumerator support for foreach loops


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<T> and IAsyncEnumerator<T> 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<T> or IAsyncEnumerator<T> 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:

This is possible because countryEnumerator exposes a public GetEnumerator() method (which is an extension) that is recognized by the foreach statement, example:

Practical isn’t it ? 😉

Written by


Anthony is a specialist in Web technologies (14 years of experience), in particular Microsoft .NET and learns the Cloud Azure platform. He has received twice the Microsoft MVP award and he is also certified Microsoft MCSD and Azure Fundamentals.
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