C#. Given an Enumerator, iterate till end to produce an enumerable

Question

In C#, I would like to write an extension method that would take an Enumerator<T> and give back an IEnumerable<T>. This could prove useful, for example, if I had to enumerate to some point in a list and then want a list with current element (if enumeration has started) plus the remaining elements.

Here's a simple implementation I started out with

  public static IEnumerable<T> Enumerate<T>(this IEnumerator<T> enumerator)
  {
      do
      {
          yield return enumerator.Current;
      }
      while (enumerator.MoveNext());
  }

Problem I am having is that if enumeration hasn't already started then this would add a default value of T to the sequence (as its first element). Is there any way to work around this/ without having to pass in additional arguments.

Answer 1

You need the .MoveNext() call before the yield statement.

public static IEnumerable<T> Enumerate<T>(this IEnumerator<T> enumerator)
{
    while (enumerator.MoveNext())
    {
        yield return enumerator.Current;
    };
}