Re: this should work

From	Rainer Weikusat <rweikusat@mssgmbh.com>
Newsgroups	comp.lang.perl.misc
Subject	Re: this should work
Date	2013-07-11 18:08 +0100
Message-ID	<87oba9ausa.fsf@sapphire.mobileactivedefense.com> (permalink)
References	(1 earlier) <87a9ltqw5i.fsf@sapphire.mobileactivedefense.com> <5ri2ba-85p1.ln1@anubis.morrow.me.uk> <87li5dclp5.fsf@sapphire.mobileactivedefense.com> <58v2ba-u112.ln1@anubis.morrow.me.uk> <87zjttax6o.fsf@sapphire.mobileactivedefense.com>

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Rainer Weikusat <rweikusat@mssgmbh.com> writes:

[...]

> I have no doubt that you will be able to find a way to transform the
> code such that the difference I was writing about becomes
> unmeasurable

Just in case there's any doubt about that: Ben is - of course - right
in claiming that Perl doesn't really create a new variable if the
previously created one is still available for reuse, it just puts that
back into a 'virgin' state. Which is still more work then when the
variable has been created outside of the loop. Also, it is possible to
write code such that it exploits other side-effects of the 'new
variable perl loop' to make the difference more accentuated eg

-------------
use Benchmark;

sub three()
{
    return "three";
}

sub in_loop
{
	for (0 .. 100) {
	    my $a;
	    $a = three() if $_ & 1;
	}
}

sub out_of_loop
{
	my $a;
	for (0 .. 100) {
	    $a = three() if $_ & 1;
	}
}

timethese(-2,
	  {
		in_loop => \&in_loop,
		out_of_loop => \&out_of_loop
	   });
-------------

and it is - of course - also possible to 'enhance' perl to work around
stupidly written code harder in order to catch this as well. But
making the compiler work harder in order to hide someone's mistakes
better is still not exactly what I want to have given that the amount
of work the compiler performs is also a cost wich affects me.

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this should work "George Mpouras" <nospam.gravitalsun.antispam@spamno.hotmail.anispam.com.nospam> - 2013-07-11 01:08 +0300
  Re: this should work Jim Gibson <jimsgibson@gmail.com> - 2013-07-10 15:49 -0700
    Re: this should work George Mpouras <nospam.gravitalsun.noadsplease@hotmail.noads.com> - 2013-07-11 09:42 +0300
      Re: this should work tmcd@panix.com (Tim McDaniel) - 2013-07-11 08:02 +0000
        Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 12:45 +0100
          Re: this should work George Mpouras <nospam.gravitalsun.noadsplease@hotmail.noads.com> - 2013-07-11 15:03 +0300
            Re: this should work "Peter J. Holzer" <hjp-usenet3@hjp.at> - 2013-07-11 14:52 +0200
              Re: this should work George Mpouras <nospam.gravitalsun.noadsplease@hotmail.noads.com> - 2013-07-11 16:01 +0300
                Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 14:29 +0100
        Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 14:27 +0100
          Re: this should work Peter Makholm <peter@makholm.net> - 2013-07-11 15:50 +0200
      Re: this should work Jürgen Exner <jurgenex@hotmail.com> - 2013-07-11 03:34 -0700
        Re: this should work George Mpouras <nospam.gravitalsun.noadsplease@hotmail.noads.com> - 2013-07-11 13:55 +0300
          Re: this should work Peter Makholm <peter@makholm.net> - 2013-07-11 13:57 +0200
          Re: this should work Shmuel (Seymour J.) Metz <spamtrap@library.lspace.org.invalid> - 2013-07-11 09:10 -0400
            Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 21:35 +0100
    Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 10:32 +0100
      Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 12:51 +0100
        Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 13:42 +0100
          Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 16:23 +0100
            Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 17:17 +0100
              Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 18:08 +0100
              Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 21:48 +0100
          Re: this should work Keith Keller <kkeller-usenet@wombat.san-francisco.ca.us> - 2013-07-11 10:32 -0700
            Re: this should work Jürgen Exner <jurgenex@hotmail.com> - 2013-07-11 10:48 -0700
              Re: this should work "George Mpouras" <nospam.gravitalsun.antispam@spamno.hotmail.anispam.com.nospam> - 2013-07-11 21:38 +0300
              Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 23:08 +0100
            Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 18:48 +0100
              Re: this should work Charles DeRykus <derykus@gmail.com> - 2013-07-11 12:03 -0700
                Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 22:02 +0100
                Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 23:06 +0100
                Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-12 01:04 +0100
                Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-15 13:41 +0100
                Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-15 14:07 +0100
                Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-15 15:05 +0100
                Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-15 21:02 +0100
                Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-15 23:58 +0100
                Re: this should work tmcd@panix.com (Tim McDaniel) - 2013-07-15 17:23 +0000
                Re: this should work Charlton Wilbur <cwilbur@chromatico.net> - 2013-07-15 15:40 -0400
              Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 21:58 +0100
                Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-11 23:17 +0100
                [OT] scoping Ivan Shmakov <oneingray@gmail.com> - 2013-07-12 07:50 +0000
                Re: [OT] scoping aka 'new holes in old shoes' Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-12 11:53 +0100
                [OT] engineering Ivan Shmakov <oneingray@gmail.com> - 2013-07-15 11:37 +0000
                Re: [OT] engineering Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-16 21:49 +0100
                Re: [OT] engineering Ivan Shmakov <oneingray@gmail.com> - 2013-07-17 09:27 +0000
                Re: [OT] engineering Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-17 15:53 +0100
                Re: [OT] engineering Ivan Shmakov <oneingray@gmail.com> - 2013-07-22 10:36 +0000
                Re: [OT] engineering Shmuel (Seymour J.) Metz <spamtrap@library.lspace.org.invalid> - 2013-07-23 06:43 -0400
                Re: [OT] engineering Ivan Shmakov <oneingray@gmail.com> - 2013-07-22 10:38 +0000
                Re: [OT] engineering Rui Maciel <rui.maciel@gmail.com> - 2013-07-26 10:09 +0100
                Re: [OT] scoping "Peter J. Holzer" <hjp-usenet3@hjp.at> - 2013-07-12 14:58 +0200
                Re: [OT] scoping Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-12 15:50 +0100
                Re: [OT] scoping Shmuel (Seymour J.) Metz <spamtrap@library.lspace.org.invalid> - 2013-07-12 13:34 -0400
                Re: [OT] scoping Ben Morrow <ben@morrow.me.uk> - 2013-07-12 22:04 +0100
                Re: [OT] scoping Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-13 13:13 +0100
                Re: [OT] scoping John Black <jblack@nospam.com> - 2013-07-13 20:01 -0500
                Re: [OT] scoping Ben Morrow <ben@morrow.me.uk> - 2013-07-14 03:24 +0100
                Re: [OT] scoping "Dr.Ruud" <rvtol+usenet@xs4all.nl> - 2013-07-14 10:49 +0200
                Re: [OT] scoping Ben Morrow <ben@morrow.me.uk> - 2013-07-14 13:13 +0100
                Re: [OT] scoping "Dr.Ruud" <rvtol+usenet@xs4all.nl> - 2013-07-14 17:02 +0200
                Re: [OT] scoping Ben Morrow <ben@morrow.me.uk> - 2013-07-14 22:21 +0100
                Re: [OT] scoping "Dr.Ruud" <rvtol+usenet@xs4all.nl> - 2013-07-15 02:21 +0200
                Re: [OT] scoping Xho Jingleheimerschmidt <xhoster@gmail.com> - 2013-07-14 17:04 -0700
                Re: [OT] scoping Ben Morrow <ben@morrow.me.uk> - 2013-07-15 14:12 +0100
                Re: [OT] scoping tmcd@panix.com (Tim McDaniel) - 2013-07-14 15:11 +0000
                Re: [OT] scoping "Dr.Ruud" <rvtol+usenet@xs4all.nl> - 2013-07-14 17:34 +0200
                Re: [OT] scoping Xho Jingleheimerschmidt <xhoster@gmail.com> - 2013-07-14 15:34 -0700
                Re: [OT] scoping Ben Morrow <ben@morrow.me.uk> - 2013-07-15 14:27 +0100
                Re: [OT] scoping John Black <jblack@nospam.com> - 2013-07-14 23:48 -0500
                Re: [OT] scoping Martijn Lievaart <m@rtij.nl.invlalid> - 2013-07-13 12:14 +0200
      Re: this should work David Harmon <source@netcom.com> - 2013-07-11 10:02 -0700
        Re: this should work Ben Morrow <ben@morrow.me.uk> - 2013-07-11 22:04 +0100
          Re: this should work David Harmon <source@netcom.com> - 2013-07-12 09:34 -0700
            Re: this should work Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-12 18:16 +0100
        Re: this should work "Dr.Ruud" <rvtol+usenet@xs4all.nl> - 2013-07-12 15:44 +0200
          Re: this should work David Harmon <source@netcom.com> - 2013-07-12 15:53 -0700
  Re: this should work Shmuel (Seymour J.) Metz <spamtrap@library.lspace.org.invalid> - 2013-07-11 09:14 -0400
    Re: this should work "George Mpouras" <nospam.gravitalsun.antispam@spamno.hotmail.anispam.com.nospam> - 2013-07-11 19:45 +0300

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