[ruby-core:110747] [Ruby master Feature#16796] Assigning local variables when using `case when regexp`

[milouse <noreply@ruby-lang.org>]

Issue #16796 has been updated by milouse (Étienne Deparis).


shyouhei (Shyouhei Urabe) wrote in #note-3:
> sawa (Tsuyoshi Sawada) wrote in #note-2:
> 
> That's too confusing.  The following code works today.
> 
> ```ruby
> case "str"
> in /s(.)r/ => match_data
>   match_data[1] # => "t"
> end
> ```

Not really (or at least it is not what I understand from the original request, as I felt on a similar issue today). You are just pointing out an edge case where `match_data[1]` will be `t`, not because it is actually a `MatchData` object, which first capturing group worth `t`, but just because the pattern matching feature select this branch and put the original `String` "str" onto `match_data`. Thus `match_data[1]` here only gives you the second char of the string `match_data`.

The previous example would have fail (in my understanding of the problem), with the following regexp:

```ruby
case "str"
in /(.)tr/ => match_data
  match_data[1] # => "t" instead of the expected "s"
end
```

By the way, there is in fact a very simple way to achieve the initial goal (again, from my understanding of the problem):

```
case "str"
when /s(?<mid>.)r/
  match_data = Regexp.last_match
  p match_data[:mid]
end
```

----------------------------------------
Feature #16796: Assigning local variables when using `case when regexp`
https://bugs.ruby-lang.org/issues/16796#change-100084

* Author: UlyssesZhan (Ulysses Zhan)
* Status: Rejected
* Priority: Normal
----------------------------------------
I want to use
```ruby
case "str"
when /s(?<mid>.)r/
  p mid
end
```
instead of
```ruby
case
when /s(?<mid>.)r/ =~ "str"
  p mid
end
```
I also do not like using `$1`.

This feature is extremely useful when there are a lot of `when`s.



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