From: Kristof Bastiaensen <kristof@...>
Date: 2004-09-08T22:50:51+09:00
Subject: Re: ruby-dev summary 24171-24235

Hi,

On Wed, 08 Sep 2004 18:29:22 +0900, Minero Aoki wrote:
> [ruby-dev:24203] $~ alternative
> 
>   Shugo Maeda proposed a new multiple assignment scheme to provide an
>   alternative of $~ variable.  His proposal is similar to the one of
>   Common Lisp:
> 
>     a = 1, 2, 3
>     p a   #=> 1
> 
>     *a = 1, 2, 3
>     p a   #=> [1, 2, 3]
> 
>   This rule allows to let methods return additional values without
>   breaking backward compatibility.
> 
>     idx = "foo bar".index(/oo/)      # compatible with current code idx, m
>     = "foo bar".index(/oo/)   # m = $~
> 
>     "foo bar".gsub(/oo/) do |str|     # compatible with current code
>       ....
>     end
>     "foo bar".gsub(/oo/) do |str, m|  # m = $~
>       ....
>     end
> 
>   On the other hand, this scheme breaks codes which use `auto composite'
>   feature of multiple assignment:
> 
>     h = {1=>3, 2=>9, 3=>27}
>     h.each do |pair|
>       p pair     #=> [1,3] now, but 1 by this proposal
>     end

Interesting.  
A new multiple assignment scheme will break old code anyway.
In this case you could write "h.each do |*pair|" instead.

A bigger problem would be with the following:
[[1, 3], [2, 9], [3, 27]].each do |arg1, arg2|
  p arg1.inspect  #=> [1, 3]
  p arg2.inspect  #=> nil
end
  
An idea would be to enable pattern matching of arrays inside
argument lists and l-values (� la ML or prolog):

[[1, 3], [2, 9], [3, 27]].each do |[arg1, arg2]|
  p arg1.inspect  #=> 1
  p arg2.inspect  #=> 2
end

Regards, KB