Bug #20930
Updated by k0kubun (Takashi Kokubun) 9 days ago
With --parser=parse.y:
```
$ ruby --parser=parse.y -ve '[1].each { p it; [5].each { p it } }'
ruby 3.4.0dev (2024-12-04T19:29:24Z master 3c91a1e5fd) [x86_64-linux]
1
5
$ ruby --parser=parse.y -ve '[1].each { p _1; [5].each { p _1 } }'
ruby 3.4.0dev (2024-12-04T19:29:24Z master 3c91a1e5fd) [x86_64-linux]
-e:1: numbered parameter is already used in
-e:1: outer block here
[1].each { p _1; [5].each { p _1 } }
ruby: compile error (SyntaxError)
```
The behavior It is inconsistent between it and _1.
---
<details>
<summary>Side note about mixing `_1` and `it`, which seems good</summary>
As an aside, mixing `_1` and `it` is allowed, I think this is [good](https://bsky.app/profile/eregon.bsky.social/post/3lcg4fjcf7225), they are different things so there is not much confusion there:
```
$ ruby -ve '[1].each { p _1; [5].each { p it } }'
ruby 3.4.0dev (2024-12-04T19:29:24Z master 3c91a1e5fd) +PRISM [x86_64-linux]
1
5
$ ruby -ve '[1].each { p it; [5].each { p _1 } }'
ruby 3.4.0dev (2024-12-04T19:29:24Z master 3c91a1e5fd) +PRISM [x86_64-linux]
1
5
```
</details>
---
<details>
<summary>Prism's bug, moved to: https://github.com/ruby/prism/issues/3291</summary>
```
$ ruby -ve '[1].each { p it; [5].each { p it } }'
ruby 3.4.0dev (2024-12-04T19:29:24Z master 3c91a1e5fd) +PRISM [x86_64-linux]
1
5
$ ruby -ve '[1].each { p _1; [5].each { p _1 } }'
ruby 3.4.0dev (2024-12-04T19:29:24Z master 3c91a1e5fd) +PRISM [x86_64-linux]
1
1
```
Notice the inconsistency, `it` uses the innermost block, `_1` uses the outermost block.
I think `_1` semantics are slightly better, at least `_1` behaves like a normal local variable declared in the outer block then.
Note that on 3.3.5 it was forbidden to nest `_1` which I think might be good for clarity/avoiding ambiguity:
```
$ ruby -ve '[1].each { p _1; [5].each { p _1 } }'
ruby 3.3.5 (2024-09-03 revision ef084cc8f4) [x86_64-linux]
-e:1: numbered parameter is already used in
-e:1: outer block here
[1].each { p _1; [5].each { p _1 } }
ruby: compile error (SyntaxError)
```
</details>