On 11/3/07, howa <[EMAIL PROTECTED]> wrote: > Passing parameters (in or return) during function calls: > > Pass by reference can improve performance: Array (List) , Scalar > Pass by reference can't improve performance: Hash, Object, Reference > > Is that true?
No. Passing a hash or array variable by reference will generally be more efficient than passing a large list of elements, because the reference is a single item and lists may be arbitrarily large. (Also, the data structure typically needs to be "rebuilt" after it's passed as a list, costing extra overhead.) When you're passing a single item, it's just the same as passing a scalar (every reference is a scalar, and every object is passed as a reference). So there's no advantage (and probably a disadvantage) to introducing an extra layer of referencing. But how are you going to use this information? Would you change this first sub to work like the second one? &silly_1($fred, $barney, $betty, $wilma); # four parameters my $params = [$fred, $barney, $betty, $wilma]; &silly_2($params); # one parameter It looks promising. Is the second subroutine call more efficient than the first one? Yes, it probably is. Does this style make the program run any faster? Probably not; it takes about as long to build $params as to call the sub with a list of parameters. It turns out that writing your code in the ordinary way IS the efficient way. So why not write your code in the clearest, easiest-to-maintain style? Its also worth pointing out that, unless the subroutine in question uses very few processor cycles to do its work, the time taken to pass and return parameters is probably dwarfed by the subroutine's own run time and internal sub-calling overhead. There's no point in shaving a few processor cycles off of the call itself if the execution takes thousands or millions of them. It's like using a 200-MPH racing car to do the grocery shopping. The race car is awfully fast, but it still takes about half an hour to get the groceries home every week. Performance is great, but getting the job done is the bottom line. Having said that, if you really need to know performs better, the One True Answer can always be found by writing the code more than one way and benchmarking it. Cheers! --Tom Phoenix Stonehenge Perl Training -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/
