From: "fxn (Xavier Noria)" Date: 2022-03-13T13:55:42+00:00 Subject: [ruby-core:107882] [Ruby master Bug#18622] const_get still looks in Object, while lexical constant lookup no longer does Issue #18622 has been updated by fxn (Xavier Noria). > That makes sense, I think we should improve const_get docs to says it's like module A; B; end and not A::B (which I'd think I'm not the only one to assume). Agree :). The documentation of the constants API has a lot of room for improvement. Also, lookup algorithms, you basically need to reverse engineer them (or read source code). I remember some 10 years ago in Amsterdam, talking about this, that @headius told me: "You are going through what I had to go through myself to implement JRuby". I documented quite a bit in the old Rails guide (https://guides.rubyonrails.org/v5.2/autoloading_and_reloading_constants.html#constants-refresher), because in order to understand the caveats of the old system, users had to understand how things work. Still, not a spec, the full precise details would not fulfill that didactic goal. However, let me add a nuance. The current documentation says: > Checks for a constant with the given name in mod. If inherit is set, the lookup will also search the ancestors (and Object if mod is a Module). Therefore, it is implicitly saying it is not mimicking `A::B`, because `A::B` does not check `Object` and does not check modules by hand. But I agree with you, this could be more clear. ---------------------------------------- Bug #18622: const_get still looks in Object, while lexical constant lookup no longer does https://bugs.ruby-lang.org/issues/18622#change-96824 * Author: Eregon (Benoit Daloze) * Status: Open * Priority: Normal * ruby -v: ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-linux] * Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN ---------------------------------------- There is some inconsistency here between literal constant lookup and the meta API (const_get). Lexical constant lookup no longer uses a special case for Object, and this is good as it avoids surprises: #11547 However, `const_get` still looks in Object, even though that's confusing, inconsistent and IMHO shouldn't really happen. ```ruby module ConstantSpecsTwo Foo = :cs_two_foo end module ConstantSpecs end p ConstantSpecs.const_get("ConstantSpecsTwo::Foo") # => :cs_two_foo p ConstantSpecs::ConstantSpecsTwo::Foo # => const_get.rb:9:in `
': uninitialized constant ConstantSpecs::ConstantSpecsTwo (NameError) ``` I think we should change it so both behave the same (i.e., NameError). It's like if `cd /foo/bar` would go to `/bar` if `/foo/bar` does not exist and `/bar` does. `const_get` is a meta API so it cannot know the surrounding `Module.nesting`, but so I think it should consider the receiver of `const_get` as the only nesting (so just `ConstantSpecs` in this case, not `Object`). Note this does not affect nested constants inside the `const_get` like `Foo` above (another way to look at the inconsistency that the first component is treated differently). From https://bugs.ruby-lang.org/issues/11547#note-19 -- https://bugs.ruby-lang.org/ Unsubscribe: