one of the most basic operations you can do in a program is the swapping of two variables. who here can't remember sitting in their first programming class and being taught that the proper algorithm for swapping two variables was:
#define 3 variables, 2 for storage, one for temp...
my ($a, $b, $c);

#set the two variables to some value
$a = 5;
$b = 6;

#use the temp value to swap them
$c = $a;
$a = $b;
$b = $c;

#now, $a has $b and $b has what $a had

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and then, you left feeling pretty good about yourself, until you encountered perl (and languages like it...) that alowed you to do this wonderful thing: 
($b, $a) = ($a, $b);   #swap two variables

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well, i was thinking about this, and questioned, i wonder what the great oracle of benchmark would say about this... and the results were quite suprising:
#!/usr/bin/perl -w

use strict;
use Benchmark;

my $a = rand(10);
my $b = rand(10);

sub traditional {
   my $c = $a;
   $a = $b;
   $b = $c;
}

sub non_trad {
   ($b, $a) = ($a, $b);
}

timethese (-10, { "traditional" => \&traditional,
                  "not traditional" => \&non_trad,
                  });


[ed@darkness ed]$ perl swap.pl
Benchmark: running not traditional, traditional, 
   each for at least 10 CPU seconds...

not traditional: 11 wallclock secs (10.25 usr +  0.00 sys = 10.25 CPU)
+ @ 302846.15/s (n=3104173)
traditional: 11 wallclock secs (10.83 usr +  0.00 sys = 10.83 CPU) @ 4
+91714.04/s (n=5325263)

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which basically says, in a nutshell... the traditional 3 value approach is faster... anyone care to explain to me why?

In reply to simple swap... by eduardo

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