Issue #18915 has been updated by koic (Koichi ITO). Thank you for taking the time to discuss this at the dev meeting. I realized that I had overlooked one issue. I found some existing code that defines `AbstractMethodError` with a superclass other than `ScriptError`. The impact on proprietary code is unknown, but a GitHub search shows the following results: https://github.com/search?q=%2Fclass+AbstractMethodError%2F+language%3ARuby&type=code Not all of these define a top-level `AbstractMethodError`. For example, GitLab defines `Gitlab::AbstractMethodError` as a subclass of `Exception` within its own module namespace: https://gitlab.com/gitlab-org/gitlab/-/blob/v18.10.8-ee/lib/gitlab/abstract_... However, for a top-level `AbstractMethodError`, a `TypeError` due to a superclass mismatch could occur depending on the superclass used by existing code. One possible path forward would be for applications and gems to migrate during Ruby 4.1-dev. That said, if such updates are not made, users may encounter compatibility issues. Given this, it seems worth considering whether to proceed with introducing the new class in Ruby 4.1. ---------------------------------------- Feature #18915: New error class: NotImplementedYetError or scope change for NotImplementedError https://bugs.ruby-lang.org/issues/18915#change-117583 * Author: Quintasan (Michał Zając) * Status: Open ---------------------------------------- # Abstract Introduce `NotImplementedYetError` exception that should be used in case when the codepath has not been implemented by the developer for some reason (maybe they're designing an abstract class or are designing some sort of interface to reuse later on) OR extend the meaning of `NotImplementedError` to cover those usecases so we don't have to introduce another exception # Background `NotImplementedError` is supposed to be raised `if the underlying operating system or Ruby runtime does not support them` (https://ruby-doc.org/core-3.1.2/NotImplementedError.html) However it appears that many people are misusing this exception by raising this in a superclass from which they later inherit from. I do realize that Ruby promotes duck-typing (the default RuboCop style guide has a cop for this – https://github.com/rubocop/ruby-style-guide#duck-typing). However I have seen this being discussed numerous times: * https://github.com/rubocop/ruby-style-guide/issues/458 * http://chrisstump.online/2016/03/23/stop-abusing-notimplementederror/ * https://oleg0potapov.medium.com/ruby-notimplementederror-dont-use-it-dff1fd7... * https://gitlab.com/gitlab-org/gitlab/-/issues/354314 (which I'm the author of) * https://github.com/rmosolgo/graphql-ruby/issues/2067 (here the author actually confused it with Python's `NotImplementedError`) * https://stackoverflow.com/questions/13668068/how-to-signal-not-implemented-y... # Proposal Create `NotImplementedYetError` exception OR Allow raising `NotImplementedError` in cases other than OS or Ruby runtime incompatibilities # Evaluation ### Add `NotImplementedYetError` I think a new exception is a better idea than changing the usage of an existing one just because "everyone is using it". That said it would require people to refactor their code which might prevent wider adoption of the new exception. ### Change scope of `NotImplementedError` This would require the least amount of changes possible (only a documentation change) and I believe there would be no compatibility problems whatsoever. ---Files-------------------------------- not-implemented-error-docs.patch (1.57 KB) -- https://bugs.ruby-lang.org/