From: "niku (niku _) via ruby-core" <ruby-core@...>
Date: 2025-08-31T06:42:08+00:00
Subject: [ruby-core:123144] [Ruby Bug#21558] Regexp.union with multiple regexps returns a non-shareable object (should be shareable if possible)

Issue #21558 has been updated by niku (niku _).


> Regexp.union creates a new instance, except for a single Regexp argument case.

Ah, that makes perfect sense now. Thank you for the detailed explanation.

```irb
irb(main):001> a = /a/
=> /a/
irb(main):002> a.__id__
=> 7232
irb(main):003> b = Regexp.union(a)
=> /a/
irb(main):004> b.__id__
=> 7232
irb(main):005> c = Regexp.union(a, a)
=> /(?-mix:a)|(?-mix:a)/
irb(main):006> c.__id__
=> 17912
```

> Personally, I think freezing all Regexp instances also may be nice, but that's a different story than Regexp.union.

I agree with your opinion. I'll create a new issue.

----------------------------------------
Bug #21558: Regexp.union with multiple regexps returns a non-shareable object (should be shareable if possible)
https://bugs.ruby-lang.org/issues/21558#change-114477

* Author: niku (niku _)
* Status: Feedback
* ruby -v: ruby 3.5.0dev (2025-08-30T18:24:25Z master 5c7dfe85a1) +PRISM [arm64-darwin24]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
Regexp.union returns a non-shareable object when given multiple Regex arguments. Is this expected behavior?
It would be preferable if the resulting Regexp were shareable, since single-argument `Regexp.union` does produce a shareable object.

```irb
irb(main):001> a = /a/
=> /a/
irb(main):002> b = Regexp.union(a)
=> /a/
irb(main):003> c = Regexp.union(a, a)
=> /(?-mix:a)|(?-mix:a)/
irb(main):004> Ractor.shareable?(a)
=> true
irb(main):005> Ractor.shareable?(b)
=> true
irb(main):006> Ractor.shareable?(c)
=> false
```





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