From: "matz (Yukihiro Matsumoto)" <matz@...>
Date: 2013-01-07T10:03:23+09:00
Subject: [ruby-core:51272] [ruby-trunk - Bug #7664][Rejected] Keyword arguments with `**` make code targeting 1.9 / 2.0 difficult


Issue #7664 has been updated by matz (Yukihiro Matsumoto).

Status changed from Open to Rejected

I understand your concern.  But I consider this as a driving force to jump in to 2.0.
Since we have small compatibility issues between 1.9 and 2.0, I'd suggest moving forward.

Matz.

----------------------------------------
Bug #7664: Keyword arguments with `**` make code targeting 1.9 / 2.0 difficult
https://bugs.ruby-lang.org/issues/7664#change-35237

Author: wycats (Yehuda Katz)
Status: Rejected
Priority: Normal
Assignee: 
Category: 
Target version: 
ruby -v: 2.0.0dev


You could imagine writing code that calls into a user-supplied hook:

  log("App booted", level: :info)

It is possible for both Ruby 1.9 and Ruby 2.0 users to write such a hook:

  # Ruby 1.9
  def log(string, options={})
    level = options[:level]
    puts "#{level}: #{string}"
  end

  # Ruby 2.0
  def log(string, level: nil)
    puts "#{level}: #{string}"
  end

So far so good. It's also possible for Ruby 2.0 users to handle arbitrary arguments:

  # Ruby 2.0
  def log(string, **options)
    # pass options along to other methods without explicit keyword args support
  end

However, it is not possible to *call into* methods with arbitrary arguments in a compatible way:

  # Ruby 1.9
  args = [ string ] + [ options ]
  log(*args)

  # Ruby 2.0
  log(string, **options)

Unless I'm missing something, this makes it impossible to write code that targets both Ruby 1.9 and Ruby 2.0 if you need to send arbitrary keyword arguments to a method.

Also, because `**` is new syntax, the only way to handle this problem is via eval:

  if RUBY_VERSION > "2"
    eval "log(string, **options)", __FILE__, __LINE__
  else
    args = [ string ] + [ options ]
    log(*args)
  end

This can work if you use `class_eval` to create two different versions of the method at class creation time, but it's pretty ugly even in that case.

Is there a way to make it possible to have a backwards-compatible calling signature that can target both the Ruby 1.9 and Ruby 2.0 method signatures for doing keyword arguments?


-- 
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