Fun with Iterators and state machines

re: Fun with Iterators and state machines

Sanin Saracevic — Mon, 26 Jul 2004 22:12:00 GMT

This seems like a higher-level construct of a "standard" NT Fiber. Am I missing something?

re: Fun with Iterators and state machines

R. Andrew Lamonica — Mon, 26 Jul 2004 22:20:00 GMT

Does the method have to return "IEnumerable" or can the "yield return" be used to return other values? I can see where the lack of an Iterator would make it hard for the runtime to know when to restart at the begining of the function but it might be a fun trick to play with.

B.T.W. I could just check this but I don't seem to have a version of .NET that supports this construct. Is 2.0 Beta available to the public?

re: Fun with Iterators and state machines

Nick Parker — Mon, 26 Jul 2004 22:32:00 GMT

There is an article in MSDN covering Coroutines in .NET.

http://msdn.microsoft.com/msdnmag/issues/03/09/coroutinesinnet/

re: Fun with Iterators and state machines

Matt Pietrek — Mon, 26 Jul 2004 22:46:00 GMT

Sanin: When I first looked at Iterators, I also noticed the similarity to Win32 Fibers. However, Fibers aren't used in the C# implementation.

Andrew: The Whidbey beta can be downloaded: http://lab.msdn.microsoft.com/vs2005/get/default.aspx#express

Implementing Scheme-like streams in C#?

David's blog — Tue, 27 Jul 2004 00:32:00 GMT

re: Fun with Iterators and state machines

AT — Tue, 27 Jul 2004 11:17:00 GMT

An question - Why exceptions try/catch/finaly not allowed with yeild ?

See also:
Fibers, and other mad stuff that you shouldn’t use
http://blogs.msdn.com/greggm/archive/2004/06/07/150298.aspx

Matt Pietrek on Iterators

Mike Taulty's Weblog — Wed, 28 Jul 2004 18:03:00 GMT

Matt Pietrek on How Iterators Work

.Net Security Blog — Mon, 02 Aug 2004 20:38:00 GMT

C# 2.0 Iterators

Another Tired Idea — Mon, 02 Aug 2004 23:05:00 GMT

re: Fun with Iterators and state machines

Chad Humphries — Mon, 02 Aug 2004 23:07:00 GMT

Just thought I'd say thanks for the article. I really enjoyed it!

re: Fun with Iterators and state machines

drebin — Tue, 03 Aug 2004 00:18:00 GMT

Interesting..... but I don't get it. How or why would you ever use something like this???

re: Fun with Iterators and state machines

Amit — Tue, 03 Aug 2004 03:54:00 GMT

It seems that from the ILDASM code, the current state is modified _after_ the code in the yield block executes. This means that any construct that will cause the flow of execution to shift before state modification is either not allowed or will cause problems.

Isn't it better to modify the state first and then let the yield block execute?

re: Fun with Iterators and state machines

Julian - SerialN6kCom — Tue, 03 Aug 2004 05:48:00 GMT

Thanks, for the article.

re: Fun with Iterators and state machines

Timothy — Tue, 03 Aug 2004 08:35:00 GMT

Why not use collections?

Iterators in C#, Python, and Ruby

Michael Geary — Tue, 03 Aug 2004 12:31:00 GMT

It's interesting to compare these new C# iterators with the very similar ones in Python and Ruby. There's less code involved in those languages, making the iterators easier to understand.

To see how they compare, I translated some of the sample C# iterator code to Python and Ruby:

http://mg.to/2004/08/03/iterator-cpr

re: Fun with Iterators and state machines

Matt Pietrek — Tue, 03 Aug 2004 19:07:00 GMT

Timothy and drebin: The article I linked to in the main text (http://msdn.microsoft.com/msdnmag/issues/04/05/c20/) provides a much better "big picture" view of iterators than I did in this entry.

My short answer about the usefulness of iterators is that they make it much easier to implement your data as .NET collections that work with "foreach". In the past, implementing the code to support enumerating your data could be quite complicated. Iterators also make it very easy to support multiple ways of iterating over your data (e.g., first to last, last to first, every other item, etc...)

re: Fun with Iterators and state machines

Roshan James — Wed, 04 Aug 2004 10:56:00 GMT

Here are some potentially relevant writeups -

Implementation of Iterators in C#
http://pensieve.thinkingms.com/CommentView,guid,fd10bfa8-1aeb-4353-84c8-cd80e418424f.aspx

Implementation of Closures (Anonymous Methods) in C# 2.0
http://pensieve.thinkingms.com/CommentView,guid,9fe42970-09e3-44e2-a4d0-32d63139351a.aspx

These might be relevant too -

Iterators in Ruby
http://pensieve.thinkingms.com/CommentView,guid,dd0e61ef-6fb1-4156-9d16-81c20a6aa871.aspx

Warming up to using Iterators
http://pensieve.thinkingms.com/CommentView,guid,02da61dd-1e35-4a36-b46b-aa3a605b2ad6.aspx

The ‘Big Deal’ about Iterators
http://pensieve.thinkingms.com/CommentView,guid,d355277d-a942-4a50-aa03-d68413fd459c.aspx

CLR 2.0 Closures and Environment classes that capture arity
http://pensieve.thinkingms.com/CommentView,guid,92e51a8a-4d8d-4401-beb2-8b68a019d4bb.aspx

Matt, its surprising that a hardcore systems programming person like you is writing about implementation of managed compilers, very nice :)

cheers
Roshan James

re: Fun with Iterators and state machines

Paul Ballard — Thu, 05 Aug 2004 21:29:00 GMT

Congratulations, this blog has been featured on TheServerSide.NET

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