Re: Is for(@$array_ref) construct optimized? YES!

[Aristotle]

You're preaching to the converted. :) If you use -MO=Deparse, you'll see that the for(;;) gets compiled to a while with a continue block, the latter being where the massive performance difference weighs in. Considering that the for(@array) form eradicates fence post errors from the root, there's rarely any good reason to use for(;;) in Perl.

Update: I forgot. Depending on your version of B::Deparse you may need increase the exposition level with the -x switch in order to see what things really look like to Perl under the hood.

$ perl -MO=Deparse,-x7 -e 'for($i=0;$i<=10;$i++){}'
$i = 0;
while ($i <= 10) {
    ();
}
continue {
    ++$i
}
-e syntax OK
$ perl -MB::Deparse -e' print "$B::Deparse::VERSION\n"'
0.6
$ perl -v

This is perl, v5.6.1 built for i386-linux

[...]

Makeshifts last the longest.

[Weasel]

Sorry, I just checked a situation and can not confirm your sayings. Here is my log:

D:\Work\PerlScripts\utl>perl -MO=Deparse -we "$x=[];for(@$x){}"
$x = [];
foreach $_ (@$x) {
    ();
}
-e syntax OK

D:\Work\PerlScripts\utl>perl -MO=Deparse -we "$x=[];for(;;){}"
Name "main::x" used only once: possible typo at -e line 1.
$x = [];
for (;;) {
    ();
}
-e syntax OK

D:\Work\PerlScripts\utl>perl -MO=Deparse -we "$x=[];for($i=0;$i<=$#x;$
+i++){}"
$x = [];
for ($i = 0; $i <= $#x; ++$i) {
    ();
}
-e syntax OK

This is probably version-dependent (which perl version you use?) and with less probablilty $^O-dependent (what is $^O in your case?)

I think we'll find common denominator soon.

update: after I saw your update I understood more and now I think we found that commond denominator that I've just mentioned. Thanks.

[jeffa]

On Linux with Perl5.6.0:

$ perl -MO=Deparse -we '$x=[];for($i=0;$i<=$#x;$i++){}'
$x = [];
$i = 0;
while ($i <= $#x) {
    ();
}
continue {
    ++$i
}
-e syntax OK

Screamer is right - but thanks for preaching anyway, not all of us are 'converted' just yet. ;)

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

[Weasel]

Aha! we see a difference between 5.6.0 and 5.6.1 with respect to this:

D:\Perl56\bin>perl -MO=Deparse -we "$x=[];for($i=0;$i<=$#x;$i++){}"
$x = [];
$i = 0;
while ($i <= $#x) {
    ();
}
continue {
    ++$i
}
-e syntax OK

D:\>perl -MO=Deparse -we "$x=[];for($i=0;$i<=$#x;$i++){}"
$x = [];
for ($i = 0; $i <= $#x; ++$i) {
    ();
}
-e syntax OK

Here I tried to compare 5.6.0 (I called it from 5.6.0 dir which is d:\perl56\bin in my computer) and 5.6.1 (it's in my $PATH)

update I did update to call a snippet without compile errors; but explanation of results before and after update are same