Re: this should work

Newsgroups	comp.lang.perl.misc
Subject	Re: this should work
References	<krkm21$19jd$1@news.ntua.gr> <100720131549354102%jimsgibson@gmail.com> <87a9ltqw5i.fsf@sapphire.mobileactivedefense.com> <DZSdnaZ2Y-zBeEPMnZ2dnUVZ_gqdnZ2d@earthlink.com>
From	Ben Morrow <ben@morrow.me.uk>
Organization	morrow.me.uk
Date	2013-07-11 22:04 +0100
Message-ID	<d8j3ba-va22.ln1@anubis.morrow.me.uk> (permalink)

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Quoth "Newsgroup only please, address is no longer replyable."  <bad@example.invalid>:
> On Thu, 11 Jul 2013 10:32:41 +0100 in comp.lang.perl.misc, Rainer
> Weikusat <rweikusat@mssgmbh.com> wrote,
> >Jim Gibson <jimsgibson@gmail.com> writes:
> >
> >[...]
> >
> >> foreach my $dir (qw/commands_pre commands_post/) { 
> >>   my $tmpdir = "/tmp/$dir"; 
> >>   print "$tmpdir\n" 
> >> }
> >
> >The perl compiler doesn't do invariant code motion because whether or
> >not some code is 'invariant' cannot generally be decided at compile
> >time. Because of this, the loop body above behave exactly as written
> >down: For each iteration, it creates a new my variable and assigns a
> >value to it. Unless there's a specific reason why this behaviour would
> >be desirable, such constructs should be avoided[*].
> 
> Are you really proposing that the programmer should be expected to
> write:
> 
>  {
>   my $tmpdir; 
>   foreach my $dir (qw/commands_pre commands_post/) { 
>     $tmpdir = "/tmp/$dir"; 
>     print "$tmpdir\n" 
>   }
>  }

This will, of course, be a good bit slower than with the my inside the
loop. Blocks are quite expensive, because they're one-iteration loops,
and that requires a bit of setup.

Ben

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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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