Bug #21049: Reconsider handling of the numbered parameters and "it" parameter in `Binding#local_variables`

• Status: Open
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN

[mame (Yusuke Endoh)]

Currently, Binding#local_variable* APIs wrongly handles the numbered parameters.

# 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.

"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.

[mame (Yusuke Endoh)]

• Related to Bug #20965: `it` vs `binding.local_variables` added

[matz (Yukihiro Matsumoto)]

I take all three "expected" in the first example. I'd rather wait for the request for the new (additional) APIs with real-world use-case.

Matz.

[mame (Yusuke Endoh)]

• Status changed from Open to Closed

Fixed by 993fd96ce6bb763e08207bb3d53824d5d46d07a4.

[daniel.domjan (Dániel Domján)]

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

@matz (Yukihiro Matsumoto), 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.

[mame (Yusuke Endoh)]

• Status changed from Closed to Open