[ruby-core:116265] [Ruby master Feature#19742] Introduce `Module#anonymous?`

Issue #19742 has been updated by fxn (Xavier Noria). I have all these matters in my head pretty clearly (and I am writing a book about constants), but in case someone is reading and is not used to the orthogonality of all this, you can even have a permanent set that is not reachable even when created: ```ruby M = Module.new N = M Object.send(:remove_const, :M) N::C = Class.new N::C.name # => "M::C" module N class D end end N::D.name # => "M::D" ``` The reason is that the resolution algorithms determine on which class or module **object** you are creating the constants. The answer is "in the one **stored** in the `N` constant stored in the class object stored in the `Object` constant". OK, you got an object. It has a name attribute, and from that string you derive a new string. It is all quite orthogonal. ---------------------------------------- Feature #19742: Introduce `Module#anonymous?` https://bugs.ruby-lang.org/issues/19742#change-106287 * Author: ioquatix (Samuel Williams) * Status: Open * Priority: Normal ---------------------------------------- As a follow-on <from https://bugs.ruby-lang.org/issues/19521>gt;, I'd like propose we introduce `Module#anonymous?`. In some situations, like logging/formatting, serialisation/deserialization, debugging or meta-programming, we might like to know if a class is a proper constant or not. However, this brings about some other issues which might need to be discussed. After assigning a constant, then removing it, the internal state of Ruby still believes that the class name is permanent, even thought it's no longer true. e.g. ``` m = Module.new m.anonymous? # true M = m m.anonyomous # false Object.send(:remove_const, :M) M # uninitialized constant M (NameError) m.anonymous? # false ``` Because RCLASS data structure is not updated after the constant is removed, internally the state still has a "permanent class name". I want to use this proposal to discuss this issue and whether there is anything we should do about such behaviour (or even if it's desirable). Proposed PR: https://github.com/ruby/ruby/pull/7966 cc @fxn -- https://bugs.ruby-lang.org/