[ruby-core:95787] [Ruby master Bug#16340] There are cases where `eval("_ 1")` does not refer to Numbered parameter

[eregontp@gmail.com]

Issue #16340 has been updated by Eregon (Benoit Daloze).

Status changed from Open to Rejected

I think the behavior is expected.
`_1` is a local variable in your example and eval can access local variables outside of it.

However, I don't think `_1` can work as numbered parameter inside an eval for a block outside the eval, because then we'd change the block arity dynamically.
What would be the Proc#arity of `lambda { _1 + eval("_#{rand(5)}") }.arity` ?

IMHO, `_1` shouldn't be supported inside `eval` as a numbered parameter when it refers to something outside `eval`.
So I think the current behavior is fine, and needs to be kept for compatibility if `_<n>` is used as a local variable.

Do you have any realistic use case where you would want your expected behavior?

I mark this as rejected because I believe it's unsolvable.

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Bug #16340: There are cases where `eval("_ 1")` does not refer to Numbered parameter
https://bugs.ruby-lang.org/issues/16340#change-82608

* Author: osyo (manga osyo)
* Status: Rejected
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.7.0dev (2019-11-11T10:03:43Z trunk 9d3213ac85) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------

## Steps to reproduce

1. Define local variable `_1` outside block
2. Call Numbered parameter in block
3. Call `eval("_1")` in same block


## Expected behavior

```ruby
_1 = :local_variable
proc {
  _1
  # return Numbered parameter(_1)
  eval("_1") # => :argument
}.call :argument
```


## Actual behavior

```ruby
_1 = :local_variable
proc {
  _1
  # return local variables outside block
  eval("_1") # => :local_variable
}.call :argument
```

This is strange behavior because I want to expect to reference `_1` in block.


## Note

* Return Numbered parameter if not define local variables outside block

```ruby
# _1 = :local_variable
proc {
  _1
  # Actual behavior
  # return Numbered parameter
  eval("_1") # => :argument
}.call :argument
```





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