[ruby-core:123798] [Ruby Bug#21049] Reconsider handling of the numbered parameters and "it" parameter in `Binding#local_variables`

14 Nov 2025

      Issue #21049 has been updated by daniel.domjan (Dániel Domján).

File RM-numbered-params-visible.png added
File RM-numbered-params-not-visible.png added

@matz, in RubyMine we show users the values of numbered parameters as well 
while debugging, but after this change we can no longer do so, since we don't have access to them. 

I think introducing the dedicated API proposed in this issue could be beneficial for all kinds of 
debug tooling, as it would allow developers to inspect the values of such parameters conveniently.

----------------------------------------
Bug #21049: Reconsider handling of the numbered parameters and "it" parameter in `Binding#local_variables`
https://bugs.ruby-lang.org/issues/21049#change-115199

* Author: mame (Yusuke Endoh)
* Status: Closed
* Assignee: matz (Yukihiro Matsumoto)
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
Currently, `Binding#local_variable*` APIs wrongly handles the numbered parameters.

```ruby
# Binding#local_variables includes numbered parameters that should not be visible
"foo".tap do
  _1
  "bar".tap do
    p binding.local_variables #=> expected: [], actual: [:_1]
  end
end

# Binding#local_variable_get can read numbered parameters that should not be readable
"foo".tap do
  _1
  "bar".tap do
    p binding.local_variable_get(:_1) #=> expected: NameError, actual: "foo"
  end
end

# Binding#local_variable_set can update numbered parameter
"foo".tap do
  p _1 #=> "foo"
  binding.local_variable_set(:_1, "bar") # expected: NameError, actual: updates _1
  p _1 #=> "bar"
end
```

My proposal is to stop handling numbered parameters and "it" parameter in `Binding#local_variable*` APIs.

```ruby
"foo".tap do
  _1
  binding.local_variables         #=> proposed: []
  binding.local_variable_get(:_1) #=> proposed: NameError
end
```

Here is a proof-of-concept patch.

https://github.com/ruby/ruby/pull/12601

It would be theoretically possible to fix `Binding#local_variable*` APIs to handle numbered parameters while maintaining compatibility as much as possible.
However, I think the implicit “it” parameter introduced in Ruby 3.4 poses a spec-level problem.
This is because there is no way to distinguish between the implicit “it” parameter and a true local variable named "it".

Also, I don't think numbered parameters are local variables, so I feel uncomfortable handling them by `Binding#local_variable*` APIs.

If it is absolutely necessary to access numbered parameters or "it" parameter via binding, it would be good to introduce dedicated APIs for the purpose, as:

* Binding#numbered_parameters              #=> [:_1, :_2, :_3, ...]
* Binding#numbered_parameter_get(:_1)      #=> obj
* Binding#numbered_parameter_defined?(:_1) #=> true or false
* Binding#it_get       #=> obj
* Binding#it_defined?  #=> true or false

Personally, however, I do not see the need for these APIs currently. I implemented them as proof-of-concept in PR, but I am okay that they are not introduced.

---Files--------------------------------
RM-numbered-params-visible.png (50.6 KB)
RM-numbered-params-not-visible.png (46.9 KB)

-- 
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