From: daniel@...42.com
Date: 2019-09-12T02:05:23+00:00
Subject: [ruby-core:94916] [Ruby master Misc#16157] What is the correct and *portable* way to do generic delegation?

Issue #16157 has been updated by Dan0042 (Daniel DeLorme).


> Then if you call `foo` with keywords, keywords will be passed to `bar`.  This should allow for more backwards compatible behavior with older versions of Ruby.

Ah, great! So we no longer need the RUBY_VERSION check!

I have a feeling the `pass_keywords` behavior would be appropriate for 99% of methods with an argument splat but no keywords. In that case maybe it would make things simpler to turn on the behavior by default and turn it off via `do_not_pass_keywords` or something? Just a thought.

> All differences are due to empty keyword splats not being passed as positional arguments in 2.7, and I would consider them at least undesired behavior in 2.6, if not an outright bug.

Maybe often undesired, but not always. Without that behavior, `opt_arg_o(hash, **opt)` would pass `hash` as kwarg in 2.6.


----------------------------------------
Misc #16157: What is the correct and *portable* way to do generic delegation?
https://bugs.ruby-lang.org/issues/16157#change-81530

* Author: Dan0042 (Daniel DeLorme)
* Status: Open
* Priority: Normal
* Assignee: 
----------------------------------------
With the keyword argument changes in 2.7 we must now specify keyword arguments explicitly when doing generic delegation. But this change is not compatible with 2.6, where it adds an empty hash to the argument list of methods that do not need/accept keyword arguments.

To illustrate the problem:

```ruby
class ProxyWithoutKW < BasicObject
  def initialize(target)
    @target = target
  end
  def method_missing(*a, &b)
    @target.send(*a, &b)
  end
end

class ProxyWithKW < BasicObject
  def initialize(target)
    @target = target
  end
  def method_missing(*a, **o, &b)
    @target.send(*a, **o, &b)
  end
end

class Test
  def args(*a)   a  end
  def arg(a)     a  end
  def opts(**o)  o  end
end
                                          # 2.6        2.7              3.0
ProxyWithoutKW.new(Test.new).args(42)     # [42]       [42]             [42]        ok
ProxyWithoutKW.new(Test.new).arg(42)      # 42         42               42          ok
ProxyWithoutKW.new(Test.new).opts(k: 42)  # {:k=>42}   {:k=>42} +warn   [{:k=>42}]  incompatible with >= 2.7
ProxyWithKW.new(Test.new).args(42)        # [42, {}]   [42]             [42]        incompatible with <= 2.6
ProxyWithKW.new(Test.new).arg(42)         # error      42               42          incompatible with <= 2.6
ProxyWithKW.new(Test.new).opts(k: 42)     # {:k=>42}   {:k=>42} +warn   {:k=>42}    must ignore warning? cannot use pass_positional_hash in 2.6
```

I don't know how to solve this, so I'm asking for the **official** correct way to write portable delegation code. And by **portable** I mean code that can be used in gems that target ruby 2.6 and above.




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