Misc #21299: Proposal: Remove `continuation` gem

• Status: Closed
• Assignee: -

[ianks (Ian Ker-Seymer)]

Continuations have been obsolete since Ruby 2.2 but still add complexity to the core codebase. I propose removing all continuation support from Ruby Core.

Reasons

Simplifies fiber code

• Current fiber code in cont.c is complicated by shared logic with continuations
• Removing continuations will simplify stack management, context switching, and reduce edge cases
• Ultimately leading to: cleaner code, easier maintenance, possible performance improvements

Low compatibility risk

• Major libraries (e.g., Metasploit) stopped using continuation years ago
• Projects needing this functionality have found workarounds (e.g., hyperion_http simulates callcc)
• TruffleRuby does not support continuations, yet maintains high compatibility

Proposed steps

1. Remove the continuation gem from default gems.
2. Delete all continuation-specific code in cont.c.
3. Add a stub gem that raises an exception if continuations are used.
4. Optionally document alternative approaches for users who still need this feature.

[ianks (Ian Ker-Seymer)]

• Subject changed from Proposal: Remove Continuation Feature from Ruby Core to Proposal: Remove `continuation` gem

[ianks (Ian Ker-Seymer)]

• Assignee deleted (ioquatix (Samuel Williams))

[mame (Yusuke Endoh)]

• Is duplicate of Feature #10548: remove callcc (Callcc is now going obsoleted. Please use Fiber.) added

[mame (Yusuke Endoh)]

• Status changed from Open to Closed

Please don't take callcc away from Ruby.

I would like to express my strong and careful opposition to the proposal to remove Kernel#callcc from Ruby. The proposal may seem minor to some, but to me, it would take away something quietly powerful and meaningful.

Here's why I believe callcc should stay.

1. callcc is an example of the soul of Ruby's expressive freedom

Ruby is not just a practical language; it's a language of joy, curiosity, and freedom. While I agree that callcc should not be used in most production code today, it is a rare and beautiful tool that shows what Ruby can do when it stretches.

Ruby has always prided itself on expressive freedom and linguistic diversity. I believe callcc is a small but symbolic part of that spirit.

2. Educational and research value

Continuations are one of the essential topics in programming language theory. They are very much alive in textbooks, lectures, university courses, and online materials that explore language design and control flow.

Many textbooks, lecture slides, blogs, and academic papers contain Ruby sample code using callcc. If this feature is removed, these resources will no longer work as-is, resulting in a subtle but real loss of educational compatibility. This could undermine Ruby's usefulness in academic and exploratory learning contexts.

That's not just a technical loss. It's a cultural one.

3. A foundation for experimentation and extension

Though rare in practical use, low-level features like callcc serve another important role: they enable experimentation.

From custom control structures and coroutine implementations to experimental asynchronous models, callcc has historically been used as a flexible foundation for building and exploring such constructs. Even if not widely used, its presence preserves the possibility of exploration, which is very much in line with Ruby's identity as a fun and expressive language.

Languages grow not only by trimming, but also by leaving space for the unexpected.

4. Once it's gone, we may not get it back

Removing features isn't just subtraction -- it's amputation. Even a niche, lightly-used feature like callcc is part of Ruby's story. Once it's removed, bringing it back would be difficult, and the community knowledge around it would fade.

While simplification and maintenance are important, we must not ignore the invisible value of historical, philosophical, and educational richness that would be lost along the way.

We should always ask: Is the gain really worth what we lose? In this case, I believe the answer is no.

Conclusion

callcc is not primarily for production code. It exists for education, research, experimentation, and the spirit of expressive programming. Retaining it means preserving an important facet of Ruby's personality.

That is why I say a wholehearted NO to its removal.

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*Note: This proposal is a duplicate of Feature #10548, where a discussion has already taken place. So I close this ticket as a duplicate.