Issue #21126 has been updated by byroot (Jean Boussier). I was about to write the same thing as @jeremyevans0, the `default_proc` doesn't necessarily mutate the hash, hence dropping it on freeze isn't correct. ---------------------------------------- Feature #21126: Drop default_proc when Hash#freeze is called for better Ractor support https://bugs.ruby-lang.org/issues/21126#change-111809 * Author: osyoyu (Daisuke Aritomo) * Status: Open ---------------------------------------- Hash instances with default_proc set cannot be sent/moved across Ractors, even if they are frozen. Consider the following code. Using a default proc to set an empty Array is a very common pattern, even introduced in the docs. ```ruby h = Hash.new {|h, k| h[k] = [] } h[:foo] << 1 h.freeze Ractor.new(h) {|h| p h }.take # <internal:ractor>:282:in 'Ractor.new': allocator undefined for Proc (TypeError) ``` https://docs.ruby-lang.org/en/3.4/Hash.html#class-Hash-label-Default+Proc One must explicitly call `h.default_proc = nil` before sending the hash to another Ractor. This isn't the most friendly way for the programmer since (1) it is not easy to spot that the default hash is rendering the Hash unsendable, and (2) `Hash#default_proc=` isn't a widely known API anyway (at least from my perspective). ## Proposal Automatically drop the `default` `default_proc` when Hash#freeze is called. They have little use after the Hash gets frozen. Nevertheless, it should be pointed out that this is an incompatibility for `Hash#default` `Hash#default_proc` -- they currently return the original value, but they will return `nil`. Patch: https://github.com/ruby/ruby/pull/12717 Dropping the default_proc on `Hash#freeze` will also be nicer for `Ractor.make_shareable` users, since it does not require users to find the particular Hash with the default_proc buried somewhere. -- https://bugs.ruby-lang.org/