paymon at paymon at
Thu Nov 30 05:17:40 CST 2000

okay, so it's not worth it then, unless I'm passing the array from hell.
Point taken and being poked as we speak.


On Thu, Nov 30, 2000 at 11:08:32AM +0000, Pap Taylor wrote:
> Two things Paym,
> You need to sign up from your work address if you want to post from
> there. southampton-pm has a members only submission thing in action.
> Onto your question:-
> --question
> Anyway here's me spak ladened question my old muckers.
> How does perl pass things in functions?
> E.g.
> $poo = "Bad shagging data structure";
> &myfunct($poo);
> sub myfunct
> {
> Whatever oooh the pain.
> ...
> ...
> }
> Now, does perl pass the information as a reference or does it copy the
> whole thing. In other words would I make my scripts more efficient by
> passing everything by reference?
> Over to the perl meisters.
> --- question
> Perl passes things by copy. It has to. As you know, when Perl calls a
> function, all arguments are passed as a parameter array.
> Perl will create the parameter array as a copy of the original
> data. Passing things by reference will allow subroutine modifications to
> persist after the scope of the sub.
> As for speed, somewhat difficult to say. If you do pass references, you
> obviously don't need to return stuff. If you're returning a scalar, Perl
> would create a temporary scalar behind the scenes before it arrived in your
> return value. If you return an array, Perl will create an temporary array
> to shift the stuff into the values you're assigning the result of the
> function to.
> Yadda yadda yadda.
> It would seem that by passing references, you'd stop Perl from needing to
> create this temporary values. But you'd be wrong. Perl will return
> implicitly if it doesn't return explicitly. It'll return the last thing
> evaluated by default, e.g. the result of the print function or the if
> statement. So whether you return explicitly or not, Perl will still return
> something, even if it's delivering the value to void.
> Remember, that even if you passed your args as refs, Perl would still
> endure the overhead of creating your parameter array.
> The /only/ time I use references to function calls is when there's a damn
> good reason ( i.e. passing nested structures - or multiple lists or hashes
> ). If you're after passing scalars, it isn't worth the bother. Remember
> that each of your refs is a scalar too, and will cause almost as much overhead.
> And I do hope you're using named parameters....
> P

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