[ruby-core:123655] [Ruby Bug#21662] Variables other than those in the conditional score are replaced.

3 Nov 2025


      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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