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.

Is there any reason why you have to use yield?

svick
– svick

2012-11-06 18:38:26 +00:00
Commented Nov 6, 2012 at 18:38 — svick
– svick, Commented Nov 6, 2012 at 18:38

m0sa · Accepted Answer · 2012-11-03 20:31:51Z

15

Use the yield break statement:

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

answered Nov 3, 2012 at 20:31

m0sa

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1 Comment

Josell Over a year ago

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

Raúl Otaño · Accepted Answer · 2012-11-06 18:49:42Z

3

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...

edited Nov 6, 2012 at 18:49

answered Nov 3, 2012 at 20:29

Raúl Otaño

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2 Comments

user57508 Over a year ago

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

Raúl Otaño Over a year ago

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

Lukas Winzenried · Accepted Answer · 2012-11-06 22:54:34Z

2

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

edited Nov 6, 2012 at 22:54

answered Nov 3, 2012 at 20:30

Lukas Winzenried

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1 Comment

Zaid Masud Over a year ago

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

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