[ruby-core:106660] [Ruby master Feature#17785] Allow named parameters to be keywords

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


Eregon (Benoit Daloze) wrote in #note-17:
> because one cannot know if `__params__` would be used, potentially in an `eval` or aliases or so

I agree, with that kind of complexity it wouldn't make sense. But I wasn't thinking of anything so complicated. If the token is lexically present in the method body, assign it a hash of the keyword arguments, just like a local variable. The allocation/cost is only for methods that use it. `eval("__params__")` is simply not supported. To me that's perfectly fine. Sort of like how `eval("v=42"); v` results in undefined `v` error. 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.


----------------------------------------
Feature #17785: Allow named parameters to be keywords
https://bugs.ruby-lang.org/issues/17785#change-95332

* 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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