[ruby-core:105630] [Ruby master Feature#16456] Ruby 2.7 argument delegation (...) should be its own kind of parameter in Method#parameters

Issue #16456 has been updated by Eregon (Benoit Daloze).


Since #18011 was fixed it seems unlikely to change again.

Regarding detection, in the light of https://github.com/ruby/ruby/pull/4961 it seems best to detect `(...)` via `parameters.include?([:block, :&])`.

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Feature #16456: Ruby 2.7 argument delegation (...) should be its own kind of parameter in Method#parameters
https://bugs.ruby-lang.org/issues/16456#change-94120

* Author: aaronc81 (Aaron Christiansen)
* Status: Open
* Priority: Normal
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A method defined with `...` as its parameter list is equivalent to one defined with `*args, &blk`, according to `Method#parameters`.

```ruby
def foo(...); end
p method(:foo).parameters
# => [[:rest, :*], [:block, :&]]
```

Even in Ruby 2.7, `...` and `*args, &blk` are not *quite* equivalent as the latter may produce a warning where the former does not. In Ruby 3.0 and beyond, `...` and `*args, &blk` will have a substantial semantic difference. Due to this, I don't consider the current behaviour of `Method#parameters` particularly ideal when dealing with methods using this new syntax.

If the goal of `...` is to be a "delegate everything" operator, even when parameter passing is changed like in Ruby 3.0, I would propose that `Method#parameters` considers it a unique type of parameter. For example:

```ruby
def foo(...); end
p method(:foo).parameters
# => [[:delegate, :"..."]]
```



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