[ruby-core:124925] [Ruby Feature#21942] Allow reading class variables from non-main Ractors

5 Mar 2026

      Issue #21942 has been updated by tenderlovemaking (Aaron Patterson).

I sent a patch [here](https://github.com/ruby/ruby/pull/16308)

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Feature #21942: Allow reading class variables from non-main Ractors
https://bugs.ruby-lang.org/issues/21942#change-116583

* Author: tenderlovemaking (Aaron Patterson)
* Status: Open
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It's very common in Rails applications to use class variables, and today class variables aren't even allowed to be read inside a Ractor:

```ruby
class Foo
  # This is NOT allowed to be read in non-main Ractors
  @@bar = 123
  def self.bar; @@bar; end

  # This is allowed to be read in non-main Ractors
  @baz = 123
  def self.baz; @baz; end
end

# This is OK
Ractor.new {
  p Foo.baz
}.value

# Exception here
Ractor.new {
  p Foo.bar
}.value
```

Output is like this:

```
test.rb:4:in 'Foo.bar': can not access class variables from non-main Ractors (@@bar from Foo) (Ractor::IsolationError)
	from test.rb:10:in 'block in <main>'
```

Can we allow shareable values to cross the Ractor boundary, similar to class instance variables?

Just for reference, the Rails code in question is [here](https://github.com/rails/rails/blob/371cbc9711b0b1fdadc186739c507b88ec0f288b...).

-- 
https://bugs.ruby-lang.org/