From: "jeremyevans0 (Jeremy Evans) via ruby-core" <ruby-core@...>
Date: 2024-03-04T17:46:57+00:00
Subject: [ruby-core:117054] [Ruby master Bug#20319] Singleton class is being frozen lazily in some cases

Issue #20319 has been updated by jeremyevans0 (Jeremy Evans).


Eregon (Benoit Daloze) wrote in #note-3:
> I think Kernel#freeze should only freeze the object itself, which means instance variables (and internal state if core/TypedStruct object) cannot be changed.
> That would be both more consistent semantically and more efficient, while avoiding weird cases like the above.

I disagree.  If you do not freeze the object's singleton class, then you can define or undefine any method in the singleton class, which is almost the same as being able to modify the object (from a Ruby perspective, not a C perspective).

However, redefining methods in the singleton class of the singleton class of the object does not allow you to modify the object, it only allows you to modify the object's singleton class.  However, as the object's singleton class is frozen, we still should prevent it.

This bug should be fairly simple to fix by having `Kernel#freeze` go up the singleton class chain and freeze all currently instantiated singleton classes.

----------------------------------------
Bug #20319: Singleton class is being frozen lazily in some cases
https://bugs.ruby-lang.org/issues/20319#change-107128

* Author: andrykonchin (Andrew Konchin)
* Status: Open
* ruby -v: 3.2.2
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
I've noticed suspicious behaviour (it doesn't affect anything in practice for me though) when an object becomes frozen only its own singleton class becomes frozen immediately.

A singleton class of the object immediate singleton class becomes frozen lazily after `#singleton_class` method call:

```ruby
o = Object.new
klass = o.singleton_class.singleton_class

o.freeze

puts klass.frozen?                              # false <== here we expect true
puts o.singleton_class.singleton_class.frozen?  # true
puts klass.frozen?                              # true
```

I would expect all created (and visible to user) singleton classes in an object singleton classes chain to become frozen immediately when the object gets frozen.




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