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Do Ruby::Box dream of Modular
Monolith?
joker1007 (Repro株式会社)
Rubykaigi 2026 LT
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self.inspect
橋立友宏 (@joker1007)
Repro inc.
Chief Architect
I love , , and Karaoke
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Gold Sponsor
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I come from
Asakusa(.rb)
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Ruby::Box comes!!
It's very interesting feature!!
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Have you touched Ruby::Box?
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I tried to use Ruby::Box
on Ruby on Rails.
I want to separate the domain logic by Ruby::Box.
To achieve a fully independent modular monolith.
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And It works!!
(minimal and not practical)
However, it required a few workarounds.
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Demo time!!
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Yeah!!
The class space is separated for each
URL!!
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Good parts (?) of Ruby::Box
Ruby::Box instances can freely reference one another.
In other words, a class in one box can be inherited by a class in
another box.
Of course, you can also prepend or include modules in another
box.
see. Ruby::Box ダイジェスト紹介（Ruby 4.0.0 新機能） -
STORES Product Blog
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How it works
There are 2 boxes.
module BoxA
def foo
puts "BoxA" + Ruby::Box.current.inspect
super
end
end
module BoxB
def foo = puts "BoxB" + Ruby::Box.current.inspect
end
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A = Ruby::Box.new; A.require_relative "box_a"
B = Ruby::Box.new; B.require_relative "box_b"
class Foo
prepend A::BoxA
include B::BoxB
def foo
puts "Main" + Ruby::Box.current.inspect
super
end
end
Foo.new.foo # =>
returns:
BoxA#
Main#
BoxB#
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Just by calling super
you can
seamlessly switch between
the Box.
dangerous (interesting)!!
By the way, tagomoris-san
said.
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Applying to Rails
A controller within a box inherits ApplicationController
in the
main box.
You can evaluate controller and model logic within the child box,
And once the controller logic is complete, transparently transfer
process to the controller running in the main box.
Render views in the main box.
Views invoke model method, the logic works on the child box.
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Thank you tagomoris-san!!
Ruby::Box is fun!!
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What you need to get started
For now, we need to apply a patch to zeitwerk
we need to override Ruby::Box#require
to work automatic
module generation.
Otherwise, if you run it with RUBY_BOX=1
, it can't load rails
components.
This issue is related.
https://bugs.ruby-lang.org/issues/21830
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By the way, can't we use Ruby::Box
with Rails::Engine?
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It crashes for now
require
fails to execute in the first place.
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Actually, this demo app crashes with
a SEGV quite often when it starts up.
I recommend ruby-4.0.2 to run this
sample.
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Things I want related to Ruby::Box
require
doesn't crash
Ruby::Box#name
: Box#inspect
is confusing. I want to rename it
to make it clearer.
Ruby::Box#fork
: I want to create a box while retaining the
LOADED_FEATURE that has already been required in the base
box.
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Difficulties
How to coordinate zeitwerk.
When you cross between boxes, it becomes unclear which
box the autoload require
is being executed in.
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Conclusion
Currently, it is possible to run Ruby::Box on Rails.
However, it’s very minimal and very experimental.
Still, the way Box works is really interesting!!
I can sense its potential!!
Let's try to use Ruby::Box and play around with it!!
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For more details
at the 松江Ruby会議.
Stay Tuned!!
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