How can yield return statement return no elements?

Question

I'm practicing deletion of nodes on a binary search tree, and I created a special type for null links (NullNode) using null pattern, so I can add some desirable behaviour to "null" types. Both Node type and Nullnode type share the same INode interface, which includes recursive methods.

The INode interface includes IEnumerable recursive methods por PreOrder, InOrder and PostOrder traversal, but I don't want NullNode to return any element (through yield return statements).

What can I do?

I know that I can use an impossible if-condition and then put there a yield return statement in the method, but I don't think this solution is good. There should be a better approach.

Niche

Is there any reason why you have to use yield? – Bollix

Answer 1

Use the yield break statement:

private static IEnumerable<INode> YieldEmpty()
{
    yield break;
}

Heart

Thank you! I used to believe the the yield break statement would stop the whole iterator, but now I understand it better. – Niche

Answer 2

Had you tried returning something like this for no returning nothing (or an empty enumerator):

return Enumerable.Empty<T>();

Or maybe using yield break; can be an alternative for exit yields loops. Hope this could help you...

Poetry

The correct syntax is Enumerable<T>.Empty()... An interface can not have a static method – Dangerous

Thanks also, but I'm not in my machine. LinkPad is great! – Bootjack

Answer 3

private static IEnumerable<T> ReturnNoElements()
{
   return Enumerable.Empty<T>();
}

Karajan

Since IEnumerable<T> is a interface, it cannot be newed – Bernstein