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Misc #16157

open

What is the correct and *portable* way to do generic delegation?

Added by Dan0042 (Daniel DeLorme) over 4 years ago. Updated over 4 years ago.

Status:
Open
Assignee:
-
[ruby-core:94860]

Description

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:

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.


Related issues 4 (2 open2 closed)

Related to Ruby master - Feature #14183: "Real" keyword argumentClosedActions
Related to Ruby master - Misc #16188: What are the performance implications of the new keyword arguments in 2.7 and 3.0?Openjeremyevans0 (Jeremy Evans)Actions
Related to Ruby master - Feature #16253: Shorthand "forward everything" syntaxClosedActions
Related to Ruby master - Feature #16897: General purpose memoizer in Ruby 3 with Ruby 2 performanceOpenActions
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