[ruby-core:113999] [Ruby master Feature#19742] Introduce `Module#anonymous?`

Issue #19742 has been updated by rubyFeedback (robert heiler).


> I don't think Rails should monkey patch Module in this way either.

This may be a problem with some of rails idioms, e. g. how HashWithIndifferentAccess
arose, to give one example. While one may understand the use case (not having to
care about same-named key strings and key symbols), it can be confusing when the
terminology does not match e. g. matz's expectation or terminology.

To the actual topic: this is the first time I heard about "permanent?". I think I 
heard about anonymous modules before, but never ".permanent?()". For the purpose
of the proposal it may be easier to ignore .permanent? altogether and just focus
on the question of the usefulness / use case of "Module#anonymous?". (I have no
particular opinion on whether it is needed or not; in my own code I rarely have 
unnamed things, not even using Class.new either. I try to keep meta-programming
as simple as possible to avoid my poor brain having to figure out what I did 
months ago with some spaghetti code.)

----------------------------------------
Feature #19742: Introduce `Module#anonymous?`
https://bugs.ruby-lang.org/issues/19742#change-103657

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
----------------------------------------
As a follow-on <from https://bugs.ruby-lang.org/issues/19521>, 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



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