[ruby-core:111621] [Ruby master Bug#19270] Constants lookup and a singleton class issue

Issue #19270 has been updated by Eregon (Benoit Daloze).

Status changed from Open to Closed

@alanwu By `attached_object_class` you mean `a.class` so `A`?

Constant lookup behaves lexically, here the scopes around method `c` are `A` and top-level/Object.
So here it looks in `A`, then `Object`, then ancestors of A. It never looks in subclasses of A (and `klass` is a subclass of A).

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Bug #19270: Constants lookup and a singleton class issue
https://bugs.ruby-lang.org/issues/19270#change-100992

* Author: andrykonchin (Andrew Konchin)
* Status: Closed
* 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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