[ruby-core:106668] [Ruby master Feature#17785] Allow named parameters to be keywords

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


matheusrich (Matheus Richard) wrote in #note-18:
> Eregon (Benoit Daloze) wrote in #note-17:
> Yeah, that's really not ideal. Do you think a special syntax (like `\class`, for example) would be less complex for Ruby implementations?

Yes, then it's only complexity in the lexer and everything else would work unchanged.
The Oz language for instance has `'reserved'` which works like `\class` above.
It's also much simpler conceptually, just help the lexer understand what you want, then everything keeps working as before.
The parser doesn't even need to know about it, it'll just see a identifier token instead of a keyword token.

Dan0042 (Daniel DeLorme) wrote in #note-19:
> In all honesty I can't understand why anyone would want to support such an edge case of eval when it results in so much complexity that is simply not needed for the normal case.

Consistency and referential transparency (anything that works outside eval should work inside eval, true for most things in Ruby).

----------------------------------------
Feature #17785: Allow named parameters to be keywords
https://bugs.ruby-lang.org/issues/17785#change-95341

* 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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