Iterating through a list is more efficient than looping over an index variable. This is because all the index keeping is done internally, where as the index variable solution has to do a lot of external operations (see. more CPU time).

Also you can't accidentally offset the index within the iterative code e.g 

for(my $i = 0; $i < @ARGVl $i++) {
    if($ARGV[$i] =~ /meets some condition/) {
        # ack! the index has been offset
        $i += 2;
    }
}

[download]
Compared to 
for my $i (0 .. $#ARGV) {
    if($ARGV[$i] =~ /meets some condition/) {
        # doesn't matter as $i will be set again in the next iteration
        $i += 2;
    }
}

[download]
This works both ways however as you may want to intentionally affect the offset, but you're possibly better off using a while loop in the first place.

Here's a quick benchmark for those in need of speed 

use Benchmark qw(cmpthese); 
my @list = 1..10000;
my $r;

cmpthese(-10, {
    cstyle => sub {
        for(my $i = 0; $i < @list; $i++) {
            $r = $list[$i];
        }
    },
    perlstyle => sub {
        for my $i (@list) {
            $r = $i;
        }
    }
});

__output__

Benchmark: running cstyle, perlstyle, each for at least 10 CPU seconds
+...
    cstyle: 15 wallclock secs (10.57 usr +  0.05 sys = 10.62 CPU) @ 36
+.06/s (n=383)
 perlstyle: 15 wallclock secs (10.10 usr +  0.03 sys = 10.13 CPU) @ 86
+.77/s (n=879)
            Rate    cstyle perlstyle
cstyle    36.1/s        --      -58%
perlstyle 86.8/s      141%        --

[download]

HTH

_________
broquaint

update: added benchmark because it's just so darned easy

In reply to Re: for ( ; ; ) vs for ( .. ) by broquaint
in thread for ( ; ; ) vs for ( .. ) by Popcorn Dave

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