[ruby-core:95339] [Ruby master Misc#16157] What is the correct and *portable* way to do generic delegation?

[eregontp@gmail.com]

Issue #16157 has been updated by Eregon (Benoit Daloze).


jeremyevans0 (Jeremy Evans) wrote:
> It certainly could.  I believe the idea of removing it after Ruby 2.6 is EOL is that gems that work on supported Ruby versions could continue to have a single method definition.  That method definition may need to change if `ruby2_keywords` is removed, though.

As we've seen countless times on bug trackers of many gems, many gems need to support Ruby versions which are EOL'd, because many applications exist and are not updated to the latest Ruby on every release.
In other words, I believe MRI version EOL is not a good deadline for this.
After all, there are other distributions than MRI which might EOL at different times or explicitly support older Ruby versions.

I believe removing `ruby2_keywords` is going to break those gems if we recommend them to entirely rely on `ruby2_keywords`.
And since currently nobody knows when `ruby2_keywords` would be removed, it's a time bomb that would need every such gem to change to fix it.
I doubt anyone wants that.
I'd bet most people would prefer a bit more verbose code that will work in the future than changing code for 2.7, knowing it will break again in the future.

Unless we never remove `ruby2_keywords`, but that doesn't make sense to me:
* It's a workaround for compatibility, we should not leave it in forever.
* It is modifying the behavior of things like `*args` which is inconsistent with other methods using `*args` but not using `ruby2_keywords`, creating inconsistency.
* We should encourage new code for Ruby 3.0+ to not use such a workaround, by simply not be able to use it.
* It's slowing down every single call with a `*rest` argument and without explicit keywords.

I think it's not a good idea to propose a migration path that we know will need to change again in the future.

To the best of our abilities, I believe it is our responsibility to provide a clear replacement that will work in all future Ruby versions.
So Rubyists don't need to modify their code a second time and they don't have to drop compatibility with Ruby < 3 at the same time as changing the code for the second time.

----------------------------------------
Misc #16157: What is the correct and *portable* way to do generic delegation?
https://bugs.ruby-lang.org/issues/16157#change-82046

* 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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