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