using local and pass by reference method

bipinbalan has asked for the wisdom of the Perl Monks concerning the following question:

Dear Monks,

I given the two scripts below. the two scripts will give the same output. But in the first one, I used pass by reference and the second, I used "local".
#### Script 1 : #####

#!/usr/bin/perl -w
use strict;
&foo1;

sub foo1
{
    my $first=1;
    &foo2(\$first);
    print "$first\n";
}

sub foo2
{
    my $second=shift;
    print "$$second\n";
    $$second++;
}
[download]

#### Script 2 : #####


#!/usr/bin/perl -w
use strict;
use warnings;

&foo1;

sub foo1
{
    local $b=1;
    &foo2;
    print "$b\n";
}


sub foo2
{
    print "$b\n";
    $b++;
}
[download]

My doubt is that which program is more efficient ? Whether we can use "local" instead of "pass by reference" ?

Hoping for the reply.

Bipin Balan

Comment on using local and pass by reference method Select or Download Code

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Re: using local and pass by reference method by ysth (Canon) on Feb 11, 2008 at 11:33 UTC
Don't worry about it? I strongly doubt you'll see any difference. local() is probably more bug-prone, so of the two, I would pass by reference. By the way, to call a subroutine with no parameters, you usually want to provide empty parentheses: `&foo1();`. &subname with no parenthesis is a special form of subroutine call that you will rarely need to use, and that may bite you when used inadvertently. -- Online Fortune Cookie Search	[reply] [d/l]
Re: using local and pass by reference method by hipowls (Curate) on Feb 11, 2008 at 10:56 UTC
Efficient for what? Speed or maintainability? Assigning a reference is pretty low cost and lexical variables are slightly more efficient. It's probably much of a muchness either way but you should benchmark if you need to know. `use Benchmark; cmpthese ( -1, { local => sub { ... }, value => sub { ... }, );` [download] Personally I'd use lexical variables and if copying was expensive or I wanted to modify the arguments use $_[0] etc or Data::Alias if I refer to an argument more than once or need to document it's purpose. For example `use Data::Alias; sub sample { alias $html = $_[0]; ... }` [download]	[reply] [d/l] [select]
Re: using local and pass by reference method by stiller (Friar) on Feb 11, 2008 at 12:02 UTC
It might be that using `local` is more effective than passing by reference (but I'm almost certain it isn't, but you could benchmark that), but that use of `local` is evil. Seeing `local` is a flag, it says something about what you are doing, and that something is not supposed to be effective, but conseptually rather to temporarily alter a global/wider scope resource, with a promise to restore it when you go out of scope and without affecting others using it elsewhere. hth	[reply] [d/l] [select]
Re: using local and pass by reference method by Narveson (Chaplain) on Feb 11, 2008 at 14:55 UTC
Always use `my`. Never use `local`. The reasons are given by Dominus in Coping with Scoping.	[reply] [d/l] [select]