[ruby-core:96334] [Ruby master Feature#16432] Using `_1` inside `binding.irb` will cause unintended behavior

Issue #16432 has been updated by nobu (Nobuyoshi Nakada).


It is same as the following code without irb.

```ruby
proc {
  p eval("(1..10).map{_1+_1}") #=> [84, 84, 84, 84, 84, 84, 84, 84, 84, 84]
  _1
}.call(42)
```

This is because the `eval` code is executed at the current context exactly.
Another choice is to raise a syntax error at the runtime.




----------------------------------------
Feature #16432: Using `_1` inside `binding.irb` will cause unintended behavior
https://bugs.ruby-lang.org/issues/16432#change-83245

* Author: osyo (manga osyo)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
## Summary

Calling `binding.irb` in a block that uses `_1` and using `_1` in `irb` will cause unintended behavior.


## Steps to reproduce

1. Use `_1` in block
2. Use `binding.irb` in block
3. Use block with `_1` in `binding.irb`

```ruby
# test.rb
proc {
  binding.irb
  _1
}.call 42
```

```ruby
# binding.irb
irb> (1..10).map { _1 + _1 }
```


## Expected behavior

```ruby
irb> _1
 => 42
irb> (1..10).map { _1 + _1 }
 = > [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
```


## Actual behavior

* Refers to the `_1` of the block that called` binding.irb`

```ruby
irb> _1
 => 42
irb> (1..10).map { _1 + _1 }
 = > [84, 84, 84, 84, 84, 84, 84, 84, 84, 84]
```

I think this is an unintended behavior for the user.






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