# Concerns about removal of continuations in Ruby 2.0 **URL:** \ **Category:** Ruby\ **Created:** [November 7, 2006, 10:48am UTC](https://www.ruby-forum.com/t/concerns-about-removal-of-continuations-in-ruby-2-0/74569 "2006-11-07T10:48:31Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![alder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/a4c791/32.png) [@alder](https://www.ruby-forum.com/u/alder)\ **Post date:** [November 7, 2006, 10:48am UTC](https://www.ruby-forum.com/t/concerns-about-removal-of-continuations-in-ruby-2-0/74569/1 "2006-11-07T10:48:31Z")
1. Certain control flow structures rely on continuations: For instance, Ruby’s generator implementation requires them[1]. Generators provide the canonical - most natural and convenient - solutions for problems as typical as iterating over two or more Arrays in parallel, simple suspended execution, resumable functions, and others. 1. Existing 3rd-party packages rely on continuations: For instance, the very popular and useful ruby-breakpoint package is designed around continuations. 1. Certain possible features and packages need continuations: The most obvious example is continuations-based web frameworks like Seaside. The Ruby community has always been living on the cutting edge of web technologies. Lack of continuations might prevent Rubyists from pursuing one of the most interesting recent developments in web-programming technology. -Alder ---
**Author:** ![alder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/a4c791/32.png) [@alder](https://www.ruby-forum.com/u/alder)\ **Post date:** [November 7, 2006, 10:48am UTC](https://www.ruby-forum.com/t/concerns-about-removal-of-continuations-in-ruby-2-0/74569/2 "2006-11-07T10:48:35Z")
On Tue, 2006-10-31 at 18:08 +0900, Alder G. wrote: > 1. Certain control flow structures rely on continuations: > > For instance, Ruby’s generator implementation requires them[1]. Not any more - check out generator.rb in 1.9 (though what’ll happen if we lose green threads too, I don’t know). ---
**Author:** ![alder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/a4c791/32.png) [@alder](https://www.ruby-forum.com/u/alder)\ **Post date:** [November 7, 2006, 10:49am UTC](https://www.ruby-forum.com/t/concerns-about-removal-of-continuations-in-ruby-2-0/74569/3 "2006-11-07T10:49:23Z")
Yukihiro M. wrote: > - Ruby 1.9.1 will not have continuation, since they have lowest > priority and are difficult to implement efficiently. > > - no promise (neither positive nor negative) on continuation for > 1.9.2 or 2.0, for exact same reason above. From a JRuby perspective, we could support continuations, but with the same or greater limitations on their utility. With no continuation support at the VM level, we would need to avoid deepening the Java call stack to allow continuations to function. This isn’t too terribly difficult to do for pure Ruby code, but quite difficult and a performance hit for Java code. It’s also impossible to do with third-party libraries involved that aren’t designed with microthreading or stackless execution in mond. There are tools that can microthread existing code after-the-fact, but that’s purely experimental. Of course I don’t believe a language should be developed with platform limitations in mind, or I’d be using Groovy…but in this case the difficulty of implementing continuations efficiently, portably, and correctly with native threads and external libraries involved almost seems to outweigh their utility. But I’m not a language design maven, so I will not offer my opinion on whether continuations are a worthwhile feature. Suffice it to say I haven’t seen any _practical_ applications of continuations that couldn’t be implemented in a less abstract (but possibly more verbose) way. ---
**Author:** ![alder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/a4c791/32.png) [@alder](https://www.ruby-forum.com/u/alder)\ **Post date:** [November 7, 2006, 10:50am UTC](https://www.ruby-forum.com/t/concerns-about-removal-of-continuations-in-ruby-2-0/74569/4 "2006-11-07T10:50:11Z")
On 10/31/06, Charles Oliver N. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > limitations in mind, or I’d be using Groovy…but in this case the > difficulty of implementing continuations efficiently, portably, and > correctly with native threads and external libraries involved almost > seems to outweigh their utility. But I’m not a language design maven, so > I will not offer my opinion on whether continuations are a worthwhile > feature. Suffice it to say I haven’t seen any _practical_ applications > of continuations that couldn’t be implemented in a less abstract (but > possibly more verbose) way. I will agree that they are rarely used (at least in Ruby), but for a nice use case see wee ([http://www.ntecs.de/blog-old/Wee](http://www.ntecs.de/blog-old/Wee)) or Seeside (in smalltalk, but more active: [http://www.seaside.st/](http://www.seaside.st/)). That being said, Matz’s goal of delivering 1.9.1 without continuations makes sense as they are rarely used in Ruby (possibly due to their inefficiency and/or the richness of Ruby’s existing flow control/block semantics). pth ---
**Author:** ![alder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/a4c791/32.png) [@alder](https://www.ruby-forum.com/u/alder)\ **Post date:** [November 7, 2006, 10:49am UTC](https://www.ruby-forum.com/t/concerns-about-removal-of-continuations-in-ruby-2-0/74569/5 "2006-11-07T10:49:20Z")
Hi, In message “Re: Concerns about removal of continuations in Ruby 2.0” on Tue, 31 Oct 2006 18:08:45 +0900, “Alder G.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes: |1. Certain control flow structures rely on continuations: |2. Existing 3rd-party packages rely on continuations: |3. Certain possible features and packages need continuations: Yes, yet they are few. What I said were: - Ruby 1.9.1 will not have continuation, since they have lowest priority and are difficult to implement efficiently. - no promise (neither positive nor negative) on continuation for 1.9.2 or 2.0, for exact same reason above. ---
**Author:** ![alder](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/a4c791/32.png) [@alder](https://www.ruby-forum.com/u/alder)\ **Post date:** [November 7, 2006, 10:55am UTC](https://www.ruby-forum.com/t/concerns-about-removal-of-continuations-in-ruby-2-0/74569/6 "2006-11-07T10:55:11Z")
Yukihiro M. wrote: > - Ruby 1.9.1 will not have continuation, since they have lowest > priority and are difficult to implement efficiently. > > - no promise (neither positive nor negative) on continuation for > 1.9.2 or 2.0, for exact same reason above. An old saying in programming language design states that the toughest part of language design is knowing what to leave out. Given that, if it is decided to leave continuations out of 1.9.1, perhaps it is wiser to leave them out “forever”, or at least until Ruby 3.0. Of course, _I_ want to see them stay in “forever”, so this is all rhetorical. 🙂 Incidentally, the Carbone project (Ruby VM using the “vmgen” base) is indeed inactive – I asked the developer. I haven’t looked at the source yet, but I just might, given that.