From: "Eregon (Benoit Daloze)" <noreply@...>
Date: 2021-12-17T18:10:20+00:00
Subject: [ruby-core:106725] [Ruby master Feature#17785] Allow named parameters to be keywords

Issue #17785 has been updated by Eregon (Benoit Daloze).


Dan0042 (Daniel DeLorme) wrote in #note-21:
> Wait a sec... actually there's precedent for this. `super` does this. It forwards all arguments up the inheritance chain. And it's possible to do `eval("super")`. `__params__` is  like the first half of `super`; just collect the arguments, without the subsequent method call. So it's definitely possible (and already done), technically.

`super` (or zsuper in parser terms) does rereads all arguments.
It's already a nightmare in terms of complexity FWIW.

But `__params__(:name)` is far worse, at least zsuper only builds an array not some magic mapping from variable name to value.

Ah and `eval("super")` should probably be deprecated, it seems such a bad idea and I doubt it works well on many Ruby impls.


----------------------------------------
Feature #17785: Allow named parameters to be keywords
https://bugs.ruby-lang.org/issues/17785#change-95410

* 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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