From: fxn@... Date: 2021-07-18T09:19:09+00:00 Subject: [ruby-core:104636] [Ruby master Feature#17881] Add a Module#const_added callback Issue #17881 has been updated by fxn (Xavier Noria). Followup here. Before I started working on Zeitwerk, I benchmarked whether a TP enabled on the `:class` event had a measurable impact. Richard Schneeman and Sam Saffron ran benchmarks too. Tests said it did not, that validated the technique for explicit namespaces and gave me green light to go ahead. @k0kubun recently ran [a new synthetic benchmarks](https://gist.github.com/k0kubun/8c50a09e94720fbadd019ba7fd04a73d) with similar results and [concluded](https://twitter.com/k0kubun/status/1400497972572397569): > ... so, in summary, Zeitwerk doesn't have to change for VM, and thus we don't need new API for it. While both MJIT and YJIT have a challenge to optimize TP-enabled programs, :class events could be a special case which is easier to optimize at least than :line. I'll work on it. I am told YJIT works fine with Zeitwerk (right @byroot?), and MJIT will work on it. So, as far as Zeitwerk is concerned, I believe we are fine and we do not need new APIs. This ticket could be pursued, if you like, for the sake of the Ruby language itself. ---------------------------------------- Feature #17881: Add a Module#const_added callback https://bugs.ruby-lang.org/issues/17881#change-92938 * 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: