From: "alanwu (Alan Wu) via ruby-core" <ruby-core@...>
Date: 2022-12-29T17:40:16+00:00
Subject: [ruby-core:111507] [Ruby master Bug#19270] Constants lookup and a singleton class issue

Issue #19270 has been updated by alanwu (Alan Wu).


It's expected behavior. When you have a singleton class `singleton_class.ancestors` is:

    [singleton_class, attached_object_class, ...]

In this case the lookup for starts at `A`, which is `attached_object_class`.
It goes to the right so it never searches `singleton_class`. The lookup resolves when the
constant is on `attached_object_class` and it starts at `singleton_class`:

```ruby
class A
  C = 1
end

a = A.new
klass = (class << a; self; end)
p klass::C # => 1
```

----------------------------------------
Bug #19270: Constants lookup and a singleton class issue
https://bugs.ruby-lang.org/issues/19270#change-100876

* Author: andrykonchin (Andrew Konchin)
* Status: Open
* Priority: Normal
* ruby -v: 3.1.3
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
I've noticed that a constant declared in a singleton class may be not visible on an object:

```ruby
class A
  def c; C; end
end

a = A.new
klass = (class << a; self; end)
klass.const_set(:C, 1)
a.c
# (irb):2:in `c': uninitialized constant A::C (NameError)
```

I would expect that such constant is visible and accessible on an object. It is expected and intentional behaviour?



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