Issue #21538 has been updated by jeremyevans0 (Jeremy Evans). I found a simple fix for all issues: https://github.com/ruby/ruby/pull/14412 ---------------------------------------- Bug #21538: initialize_dup not called when duping class/module https://bugs.ruby-lang.org/issues/21538#change-114460 * Author: chucke (Tiago Cardoso) * Status: Open * ruby -v: 3.4.5 * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- Not sure whether this is expected behaviour or not, but just leaving it here to start the debate on whether callbacks like `initialize_dup` are supposed to be called when a module or class is duped (the same happens with `initialize_copy` and `initialize_clone` btw): class A def initialize_dup(_) puts "dup instance" super end def self.initialize_dup(_) puts "dup class" super end end A.new.dup #=> "dup instance" A.dup #=> nothing -- https://bugs.ruby-lang.org/