Bug #16421: public_send with empty keyword arguments (Ruby version < 2.7)

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN

[zverok (Victor Shepelev)]

Probably it is something that I've just missed, so it is more a question than bug report.
In Ruby < 2.7, I'd implement "delegate everything" method as such:

def delegate(name, *args, &block)
  @something.public_send(name, *args, &block)
end

Now, while updating one of my gems to Ruby 2.7, I receive a warning (if SOME of the delegated methods accept keyword args):

class A
  def simple_method(arg)
    p arg
  end

  def kwargs_method(arg, kwarg:)
    p [arg, kwarg]
  end

  def delegate(name, *args, &block)
    public_send(name, *args, &block)
  end
end

A.new.delegate(:kwargs_method, 1, kwarg: 2) # warning: The last argument is used as the keyword parameter

OK, that's understandable!
Now, I am trying to rewrite kode to work with both 2.6 and 2.7:

class A
  def simple_method(arg)
    p arg
  end

  def kwargs_method(arg, kwarg:)
    p [arg, kwarg]
  end

  def delegate(name, *args, **kwargs, &block)
    public_send(name, *args, **kwargs, &block)
  end
end

A.new.delegate(:kwargs_method, 1, kwarg: 2)
A.new.delegate(:simple_method, 1)

It warks as expected under 2.7, but under 2.6, the last line throws:

tmp/delegate.rb:2:in `simple_method': wrong number of arguments (given 2, expected 1) (ArgumentError)

Is it something obvious that I am missing (I tried to search through the tracker, but can't detect related issues...). It there something I can do to have code working in both 2.6 and 2.7 without falling back to ruby_2keywords or if RUBY_VERSION < '2.7' (or checking for kwargs in if method(name).parameters)?..

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Closed

You should use ruby2_keywords:

  def delegate(name, *args, &block)
    public_send(name, *args, &block)
  end
  ruby2_keywords :delegate if respond_to?(:ruby2_keywords, true)

Then things will work correctly. This type of code is the reason that ruby2_keywords was introduced.

[zverok (Victor Shepelev)]

@jeremyevans0 (Jeremy Evans) yeah, thanks, I see now.