From: Dominik Bathon <dbatml@...>
Date: 2006-07-16T09:14:15+09:00
Subject: Re: Devious or what? : hacking super : should this work?

On Sat, 15 Jul 2006 23:15:05 +0200, Jeremy Henty <jeremy@chaos.org.uk>  
wrote:

> On 2006-07-15, dblack@wobblini.net <dblack@wobblini.net> wrote:
>> On Sun, 16 Jul 2006, Jeremy Henty wrote:
>>
>>> If you bind the entire argument list to a variable you can modify
>>> the list before calling "super".  Check it out:
>>
>> ...  super should be pretty transparent; for example, if an argument
>> is for some reason going to be altered in place by the original
>> method, you want that to still happen when you call the method that
>> calls super.
>
> True, but that's not what surprised me.  Given "def foo(*args) ..." I
> always expected the *members* of args to be the arguments of the
> method call (and not copies of them).  I did not expect args *itself*
> to be part of the Ruby call stack.  I assumed it was just a temporary
> object created on the fly to give me access to the method arguments.

This definitely is the case for Ruby 1.8 and I can't reproduce your  
example with 1.8.4, only with 1.9. I am not sure why this was changed.

In 1.8 the arguments are stored in a C array in the FRAME struct and when  
splatting is used a new Ruby array is created every time:

$ cat super_splat.rb
class A
   def foo(*a); p a, a.object_id; end
end

class B < A
   def foo(*a); p a, a.object_id; a.shift; super; end
end

B.new.foo(1,2,3)

$ ruby super_splat.rb
[1, 2, 3]
-604430366
[1, 2, 3]
-604430956


And even in 1.9 it actually is a different Ruby array:

$ ruby19 super_splat.rb
[1, 2, 3]
-604528228
[2, 3]
-604528338


Dominik