use Perl

• Example of why this is hard (Score:1)

  by Limbic Region (3985)

  For the benefit of others reading your journal that don't fully understand why this is probably not an easy thing to do....

  sub double { 2 * $_[0] }

  Seems straight forward enough and shouldn't have any side effects. Hrm, what if $_[0] is an alias to a tied variable. What if the FETCH method of that variable has action at a distance. Can't tell just by looking at the source :-(
  • Re:Example of why this is hard (Score:1)

    by Abigail (26) on 2006.10.27 2:24 (#51303) Journal

    I can tell you without looking at the source that there's a side-effect. $_[0] is going to be used in numerical context, so $_[0] will get its IOK flag (and its IVX value) set. (Effectively, this may turn out to be a no-op, but the potential is there).

    It's really, really hard to do anything meaningful in Perl that doesn't have side-effects.

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    Parent

    • Re: (Score:1)

      by DAxelrod (4649)

      How would these flags being set be visible to the Perl program? Does this mean simply using a variable a particular way in one expression can change how it's treated in other expressions?
      • Re: (Score:1)

        by Aristotle (5147)

        Yes. The first thing that comes to mind is that it may affect the behaviour of the bitwise ops. There are more examples of subtle effects; I can’t think of them right now, but I know I used to know about them.