From: "Jun Aruga (he / him)" <jaruga@...>
Date: 2022-10-21T15:22:35+02:00
Subject: [ruby-core:110465] Questions about anonymous rest and keyword rest argument forwarding

Hello,
I am testing new features in Ruby 3.2.0 now, and I have questions
about the "anonymous rest and keyword rest argument forwarding".

https://www.ruby-lang.org/en/news/2022/09/09/ruby-3-2-0-preview2-released/
https://bugs.ruby-lang.org/issues/18351

The example below is mentioned on the release note.

```
  def foo(*)
    bar(*)
  end

  def baz(**)
    quux(**)
  end
```

1. The "*" is called the "anonymous rest argument", and "**" is called
the "keyword rest argument", right?

2. I think the "*" and "**" themselves are not new in Ruby 3.2.0. Do
you know in which Ruby version these arguments were introduced?

```
$ cat annonymous_args2.rb
def foo(*)
  p "foo"
end

def baz(**)
  p "baz"
end

foo([1, 2])
baz(:a => 'A', :b => 'B')
```

The code works in Ruby 3.1.1.

```
$ /usr/local/ruby-3.1.1/bin/ruby annonymous_args2.rb
"foo"
"baz"
```

3.
The following code works in Ruby 3.2.0 preview2.

```
$ cat annonymous_args1_2.rb
def bar(*)
  puts "bar"
  p [*]
end

def foo(*)
  bar(*)
end

foo(1, 2, 3)
```

```
$ which ruby
/usr/local/ruby-3.2.0-preview2/bin/ruby

$ ruby annonymous_args1_2.rb
bar
[1, 2, 3]
```

But the following code doesn't work with the syntax errors. Do you
know what's wrong?

```
$ cat annonymous_args1_3.rb
def quux(**)
  puts "quux"
  p {**}
end

def baz(**)
  quux(**)
end

baz(:a => 'A', :b => 'B')
```

```
$ ruby annonymous_args1_3.rb
annonymous_args1_3.rb:3: syntax error, unexpected **arg
  p {**}
annonymous_args1_3.rb:10: syntax error, unexpected end-of-input, expecting '}'
baz(:a => 'A', :b => 'B')
```

```
$ which ruby
/usr/local/ruby-3.2.0-preview2/bin/ruby
```

Thanks!

-- 
Jun | He - Him | Timezone: UTC+1 or 2, Czech Republic
See <https://www.worldtimebuddy.com/czech-republic-prague-to-utc> for
the timezone.


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