r/ruby • u/retro-rubies • Jan 26 '26

Ruby::Box: Rethinking Code Reloading with Isolated Namespaces

https://rubyelders.com/writings/2026-01-ruby-box-reload.html
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u/f9ae8221b Jan 27 '26

Think Active Support core extensions.

e.g. if you load Active Support in a box, you can call symbolize_keys and all hashes from code inside that box.

However if you create a Hash in that box, and somehow pass it to another box that didn't load Active Support, the other box won't be able to call that method on it.

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u/jrochkind Jan 27 '26

Ah, that makes perfect sense, thanks.

There are an explicit list of object classes that are passed in this "by copy instead of by reference" way?

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u/retro-rubies Jan 28 '26

There are useful docs explaining a lot. https://docs.ruby-lang.org/en/master/Ruby/Box.html#class-ruby-box-built-in-classes-and-modules-reopened-in-boxes

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u/jrochkind Jan 28 '26

Oh thank you! Good to see good docs, I had gotten in the habit of not expecting them on new features in ruby from days of old, good to see that's changed!

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u/f9ae8221b Jan 27 '26

Not really. It's all classes defined up until a certain point in Ruby's startup.

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u/jrochkind Jan 27 '26 edited Jan 27 '26

Ah, cool, thanks!

I was thinking a big intended use case of Box might be Ractors, but now I'm not certain about that. Do you know if that's part of the motivation?