Bug #22105: Cannot initialize a WeakRef in a Ractor

• Status: Open
• Assignee: ractor
• Target version: -
• ruby -v: ruby 4.0.5 (2026-05-20 revision 64336ffd0e) +PRISM [x86_64-linux]
• Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN

[miles-georgi (Miles Georgi)]

Hey hey!

If I try to create a WeakRef in a Ractor, like in this script:

require "weakref"

Ractor.new { WeakRef.new("asdf") }.join

Then I get this error:

4.1-dev/lib/ruby/4.1.0+3/weakref.rb:40:in 'WeakRef#initialize': can not read non-shareable class variable @@__map from non-main Ractors (WeakRef) (Ractor::IsolationError)

This happens in both a local build of 4.1-dev and 4.0.5 and likely other versions.

[jhawthorn (John Hawthorn)]

• Assignee set to ractor