[ruby-core:106872] [Ruby master Feature#18351] Support anonymous rest and keyword rest argument forwarding

Issue #18351 has been updated by jeremyevans0 (Jeremy Evans).


palkan (Vladimir Dementyev) wrote in #note-8:
> @jeremyevans0 I've been working on supporting this feature for Ruby Next, and found a weird edge case:
> 
> ```
> def foo_with_pattern(*, **)
>   case some_value
>   in [0, 1, *]
>     bar(*)
>   in {a:, b:, **}
>     baz(**)
>   end
> end
> ```
> 
> As far as I understand, the delegation works here; and confusion is present, too.

My expected behavior is that `bar(*)` and `baz(**)` use the arguments to `foo_with_pattern`, not the values in the pattern match, because `*` and `**` in a pattern match are for ignoring arguments, not for capturing (`*` and `**` as parameters have always captured to support `super`).  I tested it and that is how it behaves, so the behavior matches my expectation.

However, my expectation isn't all that important, @matz's expectation is, so hopefully he can respond with how he would like it to behave.  I plan on merging the support fairly soon, but we have a lot of time to modify the behavior before the release of Ruby 3.2, should @matz desire different behavior.

----------------------------------------
Feature #18351: Support anonymous rest and keyword rest argument forwarding
https://bugs.ruby-lang.org/issues/18351#change-95682

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
----------------------------------------
I would like to add support for the following syntax:

```ruby
def foo(*)
  bar(*)
end
def baz(**)
  quux(**)
end
```

This is a natural addition after the introduction of anonymous block forwarding.  Anonymous rest and keyword rest arguments were already supported in method parameters, this just allows them to be used as arguments to other methods.  The same advantages of anonymous block forwarding apply to rest and keyword rest argument forwarding.

I've submitted a pull request implementing this syntax: https://github.com/ruby/ruby/pull/5148



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