[ruby-core:103362] [Ruby master Feature#17785] Allow named parameters to be keywords

Issue #17785 has been updated by nobu (Nobuyoshi Nakada).


duerst (Martin Dst) wrote in #note-7:
> What about finding something in between the two? E.g. even just introducing `variable_get` as an alias to `binding.local_variable_get` would make this easier to use. And if this really needs optimization, it could be done, too, but using a different argument name would solve the problem.

In built-in methods written in Ruby, we chose `__builtin.arg!(:in)` form (see timve.rb).

> With respect to `\`, it reminds me of older languages (such as m4, C, and TeX) where there's a purely string-based level below (or before) the usual structured syntax. Do we want Ruby to descend to that level? Escaping exists inside strings because you don't want the range of data you can handle with a programming language to be restricted by the syntax of the language itself. Also, escaping inside strings is frequent enough for everybody, and occurs in a very similar form across a wide range of programming languages, so that every programmer knows it. Backslashes in front of keywords would be a whole different matter.

Agree, and backslashes will be troublesome in `eval` obviously.

----------------------------------------
Feature #17785: Allow named parameters to be keywords
https://bugs.ruby-lang.org/issues/17785#change-91453

* 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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