C# 9 GetEnumerator support for foreach loops


In C#, if you want to iterate on a collection with the foreach loop, the collection must expose a public method GetEnumerator() which doesn't exist on IEnumerator and IAsyncEnumerator interfaces.

In C# 9.0, you can create an extension method that will allow you to iterate in foreach loops on those interfaces. Here is the simple extension method called GetEnumerator().

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

Now you can use IEnumerator<T> in foreach loops as shown below.

List<string> daysOfWeek = new List<string> { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday" };

IEnumerator<string> daysOfWeekEnumerator = daysOfWeek.GetEnumerator();

foreach (var country in daysOfWeekEnumerator)
{
    Console.WriteLine($"{country} is a beautiful country");
}

As you can see that daysOfWeek exposes a public GetEnumerator() which is provided as an extension method and that is recognized by the foreach statement.

Before C# 9.0, when you try to iterate with a foreach loop on a collection type IEnumerator<T> or IAsyncEnumerator<T>, you will get the following error.


Error CS1579 foreach statement cannot operate on variables of type 'IEnumerator<string>' because 'IEnumerator<string>' does not contain a public instance definition for 'GetEnumerator'