From: Rick DeNatale <rick.denatale@...>
Date: 2006-10-13T23:42:13+09:00
Subject: Re: Ruby expressions vs. values (like Perl?)

On 10/12/06, AlexG <alexg@ebi.ac.uk> wrote:


> Someone with better understanding of Ruby internals will need to
> confirm this because I may well be wrong, but I think you are correct.
> eval.c creates a temporary array out of the right-hand side (in the
> svalue_to_mrhs function I think). Page 91 of the Pickaxe (2nd Ed)
> explains this a little more. Whether or not optimising the Array away
> is possible or desirable is another question. Unless you are doing some
> pretty insane parallel assignment I wouldn't have thought it makes any
> practical difference.

Yep, that's exactly what seems to be happening.

One reason for this is so that a parallel assignment like

     x, y = y, x

works correctly.

If the interpreter simply broke that down into series of assignments
without the temporary array, then it would need to detect such cases
and handle them separately or:

    x = 1
    y = 2
#    x, y = y, x
# converted into
    x = y
    y = x

  x => 2
  y => 2

which is not what we want.


-- 
Rick DeNatale

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