From: eregontp@... Date: 2021-05-22T12:16:29+00:00 Subject: [ruby-core:103977] [Ruby master Feature#17881] Add a Module#const_added callback Issue #17881 has been updated by Eregon (Benoit Daloze). Description updated > A JIT that strip tracing code, and simply de-optimize when tracing is enabled doesn't seem that far fetched to me. Yes, and I think it makes a lot of sense to deoptimize/recompile for e.g., :line and :call events (those have a huge perf impact). But for `:class` I don't see how avoiding the check at the cost of deoptimization/recompilation would ever be worth it. ---------------------------------------- Feature #17881: Add a Module#const_added callback https://bugs.ruby-lang.org/issues/17881#change-92110 * 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 also has performance implications (albeit relatively minor), and [doesn't play well with MJIT](https://k0kubun.medium.com/ruby-3-jit-can-make-rails-faster-756310f235a). ### 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: <mailto:ruby-core-request@ruby-lang.org?subject=unsubscribe> <http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>