What is the best wayto add single element to an IEnumerable collection?

Question

I'm surprised to see that there does not appear to be a method to add a single element to an IEnumerable collection.

How can I add a single element to an IEnumerable collection?

Answer 1

You can't really add elements to an IEnumerable as it's supposed to be read only. Your best bet is either something like:

return new List<Foo>(enumerable){ new Foo() };

or

return enumerable.Concat(new [] { new Foo() });

Answer 2

The point of IEnumerable is that it's a readonly pull style collection. If you want, you can simulate an add by doing something like this:

public static IEnumerable<T> Add<T>(this IEnumerable<T> source, T additionalItem)
{
   foreach(var item in source)
   {
      yield return item;
   }

   yield return additionalItem;
}