From: "binh (binh chau) via ruby-core" <ruby-core@...>
Date: 2025-11-03T00:03:27+00:00
Subject: [ruby-core:123655] [Ruby Bug#21662] Variables other than those in the conditional score are replaced.

Issue #21662 has been updated by binh (binh chau).


nobu (Nobuyoshi Nakada) wrote in #note-1:
> I try to guesstimate your intension by telepathy.
> 
> binh (binh chau) wrote:
> > ```ruby
> >   def bug!
> >     if !bar.is_a?(Bar)
> >       bar = ''
> >     elsif bar.name == 'bar'
> >     end
> >   end
> > ```
> 
> You might had expected the third `bar` is a `Bar`.
> 
> In fact, the first `bar` in `!bar.is_a?(Bar)` is the attribute.
> But the assignment in the next line makes the local variable `bar` regardless whether this line is executed.
> So all `bar` after here in this method, including in the next `elsif` line, are this local variable, that is an empty string or `nil` (when the `elsif` condition is executed).

It looks like a trap.

----------------------------------------
Bug #21662: Variables other than those in the conditional score are replaced.
https://bugs.ruby-lang.org/issues/21662#change-115037

* Author: binh (binh chau)
* Status: Feedback
* ruby -v: 3.2.2
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
```ruby
class Bar
  attr_accessor :name
end

class Foo
  attr_accessor :bar
  def initialize(bar=nil)
    @bar = bar || Bar.new
  end

  def bug!
    if !bar.is_a?(Bar)
      bar = ''
    elsif bar.name == 'bar'
    end
  end
end

Foo.new.bug!
```



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