From: jean.boussier@... Date: 2021-05-23T10:38:21+00:00 Subject: [ruby-core:104000] [Ruby master Feature#17881] Add a Module#const_added callback Issue #17881 has been updated by byroot (Jean Boussier). > What I had in mind in the conversation in the Zeitwerk ticket was not const_added. It was a callback that gets called when a new class/module is created and after it gets its name set if defined with the class/module keywords. I see, seems like I missed that. I suppose the "ideal" API for an autoloader like Zeitwerk would be something like `Module#module_defined(name, module)`: - Would trigger on classic `module Foo::Bar` first opening. - Would trigger on `Foo::Bar = Class.new`. (This one being a current limitation with TracePoint if I'm not mistaken). - Would **not** trigger on `Foo.autoload(:Bar, "bar")`. - Would not trigger for non `Module` or `Class` constants. ---------------------------------------- Feature #17881: Add a Module#const_added callback https://bugs.ruby-lang.org/issues/17881#change-92137 * Author: byroot (Jean Boussier) * Status: Open * Priority: Normal ---------------------------------------- ### Use case Autoloaders like `zeitwerk` need a callback when a new class or module is registered in the constant table. Currently this is implemented with TracePoint's `:class` event. It works, but it is a bit unfortunate to have to use an API intended for debugging to implement production features. It doesn't feel "conceptually clean". It also [doesn't play well with MJIT](https://k0kubun.medium.com/ruby-3-jit-can-make-rails-faster-756310f235a), even though it's more of an MJIT limitation. Additionally this usage of TracePoint cause [some incompatibilities with some debuggers like `byebug`](https://github.com/deivid-rodriguez/byebug/issues/564) (even though others don't have this issue). ### Proposal I believe that if Ruby was to call `Module#const_added` when a constant is registered, Zeitwerk could get rid of TracePoint. For now I implemented it as: `const_added(const_name)` for similarity with `method_added`. But maybe it could make sense to have the signature be `const_added(const_name, const_value)`. Also since `method_removed` exists, maybe `const_removed` would need to be added for consistency. ### Links Patch: https://github.com/ruby/ruby/pull/4521 Zeitwerk side discussion: https://github.com/fxn/zeitwerk/issues/135 cc @k0kubun -- https://bugs.ruby-lang.org/ Unsubscribe: