[ruby-core:106657] [Ruby master Feature#17785] Allow named parameters to be keywords

Issue #17785 has been updated by matheusrich (Matheus Richard).


Eregon (Benoit Daloze) wrote in #note-17:
> matheusrich (Matheus Richard) wrote in #note-11:
> > Since we have `__method__`, maybe adding something like `__params__`?
> 
> I dislike this approach because it will introduce lots of complexity for Ruby implementations, and will likely make the language slower because arguments need to be retained longer than without it.
> In the worst case it could even introduce non-obvious memory leaks (because one cannot know if `__params__` would be used, potentially in an `eval` or aliases or so).
> 
> JavaScript's `arguments` is a well known PITA for implementations and often seen as hurting optimizations.

Yeah, that's really not ideal. Do you think a special syntax (like `\class`, for example) would be less complex for Ruby implementations?

----------------------------------------
Feature #17785: Allow named parameters to be keywords
https://bugs.ruby-lang.org/issues/17785#change-95329

* 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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