From: "Dan0042 (Daniel DeLorme)" <noreply@...>
Date: 2021-12-13T03:25:58+00:00
Subject: [ruby-core:106630] [Ruby master Feature#17785] Allow named parameters to be keywords

Issue #17785 has been updated by Dan0042 (Daniel DeLorme).


matheusrich (Matheus Richard) wrote in #note-11:
> Since we have `__method__`, maybe adding something like `__params__`?

I _really_ like this idea. Although I would prefer having different names for positional vs keywords, so maybe `__args__` and `__kwargs__`
This was previously suggested in #15049 (for the purpose of forwarding all keyword arguments) but it's very well suited to handling special keywords like `if`/`for`/`class`, without introducing extra syntax or special cases.

----------------------------------------
Feature #17785: Allow named parameters to be keywords
https://bugs.ruby-lang.org/issues/17785#change-95302

* Author: marcandre (Marc-Andre Lafortune)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
----------------------------------------
We should allow named parameters to be keywords and use add a trailing `_` to the corresponding variable:

```ruby
def check(arg, class:)
  arg.is_a?(class_)
end

check(42, class: Integer) # => true
```

Currently, if we want such an API we have to use `**rest`:

```ruby
def check(arg, **rest)
  class_ = rest.fetch(:class) { raise ArgumentError('missing keyword: :class')}
  if rest.size > 1
    unknown = rest.keys - [:class]
    raise ArgumentError("unknown keyword(s): :#{unknown.join(', :')})
  end

  arg.is_a?(class_)
end
```

This is very verbose, much less convenient, much less readable, prevents `steep` from generating the proper signature, etc.

We should do the same for pattern match.



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