my $var = val if (..) doesn't work properly

[p5pRT]

Migrated from rt.perl.org#6003 (status was 'resolved')

Searchable as RT6003$

[p5pRT]

From madison@transmeta.com

If a variable is declared "my" and then conditional set with
a trailing if, the value is *not* undefined if the condition isn't
met. Here's some example code​:

-------------------------
sub joe {
  # These should arguably be the same​:
  #my $x; $x = 42 if (0);
  my $x = 42 if (0);

  print "x​: $x\n";
  $x = 1001; # This setting should be lost
}

joe();
joe();
-------------------------

The first line declares the variable and then conditionally either sets
the variable or leaves it as undef.
The second line declares the variable, and conditionally either sets
the variable or leaves it as junk (most likely the previous my value)

You could argue that the "my" becomes part of the condition, so if
the condition is false, then the variable isn't scoped as a my variable,
but if that was the case the script should get an error from "use strict"

Perl Info

Site configuration information for perl 5.00503:

Configured by root at Mon Aug 30 23:08:56 EDT 1999.

Summary of my perl5 (5.0 patchlevel 5 subversion 3) configuration:
  Platform:
    osname=linux, osvers=2.2.5-22smp, archname=i386-linux
    uname='linux porky.devel.redhat.com 2.2.5-22smp #1 smp wed jun 2 09:11:51 edt 1999 i686 unknown '
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=undef useperlio=undef d_sfio=undef
  Compiler:
    cc='cc', optimize='-O2', gccversion=egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)
    cppflags='-Dbool=char -DHAS_BOOL -I/usr/local/include'
    ccflags ='-Dbool=char -DHAS_BOOL -I/usr/local/include'
    stdchar='char', d_stdstdio=undef, usevfork=false
    intsize=4, longsize=4, ptrsize=4, doublesize=8
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    alignbytes=4, usemymalloc=n, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lnsl -ldl -lm -lc -lposix -lcrypt
    libc=, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
    cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'

Locally applied patches:
    


@INC for perl 5.00503:
    /usr/lib/perl5/5.00503/i386-linux
    /usr/lib/perl5/5.00503
    /usr/lib/perl5/site_perl/5.005/i386-linux
    /usr/lib/perl5/site_perl/5.005
    .


Environment for perl 5.00503:
    HOME=/home/madison
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/madison/bin/i386-linux-libc6:/home/madison/bin:.:/usr/local/bin:/bin:/usr/bin:/usr/X11R6/bin:/usr/openwin/bin:/usr/sbin:/sbin:/usr/local/sbin:/proj/hw/bin:/proj/hw/bin/i386-linux-libc6:/cad/scripts:/usr/local/contrib/bin:.:/proj/sw/astro/tools/i386-linux-libc6/bin
    PERL_BADLANG (unset)
    SHELL=/bin/tcsh

[p5pRT]

From @pjscott

At 04​:29 PM 3/9/01 -0800, madison@​transmeta.com wrote​:

This is a bug report for perl from perlbug@​daveola.com,
generated with the help of perlbug 1.26 running under perl 5.00503.

-----------------------------------------------------------------
[Please enter your report here]

If a variable is declared "my" and then conditional set with
a trailing if, the value is *not* undefined if the condition isn't
met. Here's some example code​:

-------------------------
sub joe {
# These should arguably be the same​:
#my $x; $x = 42 if (0);
my $x = 42 if (0);

print "x​: $x\n";
$x = 1001; # This setting should be lost
}

joe();
joe();
-------------------------

This is well-known behavior and arguably not a bug. my() has compile-time
and run-time effects. Do a search for "Tom Christiansen" and "who says
Perl doesn't have statics?" and you may turn up a previous thread :-)

The first line declares the variable and then conditionally either sets
the variable or leaves it as undef.
The second line declares the variable, and conditionally either sets
the variable or leaves it as junk (most likely the previous my value)

You could argue that the "my" becomes part of the condition, so if
the condition is false, then the variable isn't scoped as a my variable,
but if that was the case the script should get an error from "use strict"

[Please do not change anything below this line]
-----------------------------------------------------------------

---
Site configuration information for perl 5.00503​:

Configured by root at Mon Aug 30 23​:08​:56 EDT 1999.

Summary of my perl5 (5.0 patchlevel 5 subversion 3) configuration​:
Platform​:
osname=linux, osvers=2.2.5-22smp, archname=i386-linux
uname='linux porky.devel.redhat.com 2.2.5-22smp #1 smp wed jun 2
09​:11​:51 edt 1999 i686 unknown '
hint=recommended, useposix=true, d_sigaction=define
usethreads=undef useperlio=undef d_sfio=undef
Compiler​:
cc='cc', optimize='-O2', gccversion=egcs-2.91.66 19990314/Linux
(egcs-1.1.2 release)
cppflags='-Dbool=char -DHAS_BOOL -I/usr/local/include'
ccflags ='-Dbool=char -DHAS_BOOL -I/usr/local/include'
stdchar='char', d_stdstdio=undef, usevfork=false
intsize=4, longsize=4, ptrsize=4, doublesize=8
d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
alignbytes=4, usemymalloc=n, prototype=define
Linker and Libraries​:
ld='cc', ldflags =' -L/usr/local/lib'
libpth=/usr/local/lib /lib /usr/lib
libs=-lnsl -ldl -lm -lc -lposix -lcrypt
libc=, so=so, useshrplib=false, libperl=libperl.a
Dynamic Linking​:
dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'

Locally applied patches​:

---
@​INC for perl 5.00503​:
/usr/lib/perl5/5.00503/i386-linux
/usr/lib/perl5/5.00503
/usr/lib/perl5/site_perl/5.005/i386-linux
/usr/lib/perl5/site_perl/5.005
.

---
Environment for perl 5.00503​:
HOME=/home/madison
LANG (unset)
LANGUAGE (unset)
LD_LIBRARY_PATH (unset)
LOGDIR (unset)

PATH=/home/madison/bin/i386-linux-libc6​:/home/madison/bin​:.​:/usr/local/bin​:/bin​:/usr/bin​:/usr/X11R6/bin​:/usr/openwin/bin​:/usr/sbin​:/sbin​:/usr/local/sbin​:/proj/hw/bin​:/proj/hw/bin/i386-linux-libc6​:/cad/scripts​:/usr/local/contrib/bin​:.​:/proj/sw/astro/tools/i386-linux-libc6/bin
PERL_BADLANG (unset)
SHELL=/bin/tcsh

[p5pRT]

From @pjscott

At 05​:18 PM 3/9/01 -0800, you wrote​:

This is well-known behavior and arguably not a bug. my() has compile-time
and run-time effects. Do a search for "Tom Christiansen" and "who says
Perl doesn't have statics?" and you may turn up a previous thread :-)

I can't find such a thread - should I be searching the web or news?

If it's not a bug, then it certainly allows for buglike behavior​:

--------------------------------------------------
#!/usr/bin/perl
use strict;

sub joe { my $x = 42 if (0); return \$x; }

my $y = joe();
my $z = joe();
$$y = 12;
printf "Hey​: $z is $$z\n";
--------------------------------------------------

This is, of course, demonstrating that joe() now has an
unintentional static variable without using any variables
outside it's own scope. I presume this is what the Tom
Christiansen post is about - do you know where I can find it?

http​://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/1999-11/msg00723.html
is talking about something else, to be sure, but it demonstrates that the
behavior you observed has been known about for some time. If it hasn't
been changed since then it's probably not considered a bug.

There's a thread on the topic itself at
http​://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2000-05/msg00686.html

[p5pRT]

From [Unknown Contact. See original ticket]

Lightning flashed, thunder crashed and Peter Scott <Peter@​PSDT.com> whispered​:
| http​://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/1999-11/msg00723.html
| is talking about something else, to be sure, but it demonstrates that the
| behavior you observed has been known about for some time. If it hasn't
| been changed since then it's probably not considered a bug.

*chuckle*
Just because it is an old bug doesn't necessarily mean it isn't a bug.
There are outstanding bugs in the database dating back to early '99, which
is when I believe we first started using the nugs database. Not that I'm
saying this is a bug, or isn't a bug. Just that age has nothing to do with
bugginess.

-spp

[p5pRT]

From @jhi

On Sat, Mar 10, 2001 at 02​:10​:13PM -0500, Stephen P. Potter wrote​:

Lightning flashed, thunder crashed and Peter Scott <Peter@​PSDT.com> whispered​:
| http​://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/1999-11/msg00723.html
| is talking about something else, to be sure, but it demonstrates that the
| behavior you observed has been known about for some time. If it hasn't
| been changed since then it's probably not considered a bug.

*chuckle*
Just because it is an old bug doesn't necessarily mean it isn't a bug.
There are outstanding bugs in the database dating back to early '99, which
is when I believe we first started using the nugs database. Not that I'm

There are also lots of bugs that are just open because nobody hasn't
verified them for validity with more recent Perls, or because they
are hard to duplicate.

saying this is a bug, or isn't a bug. Just that age has nothing to do with
bugginess.

-spp

[p5pRT]

From [Unknown Contact. See original ticket]

|
http​://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/1999-11/msg00723.html
| is talking about something else, to be sure, but it demonstrates that
the
| behavior you observed has been known about for some time. If it
hasn't
| been changed since then it's probably not considered a bug.

*chuckle*
Just because it is an old bug doesn't necessarily mean it isn't a bug.
There are outstanding bugs in the database dating back to early '99,
which
is when I believe we first started using the nugs database. Not that
I'm

There are also lots of bugs that are just open because nobody hasn't
verified them for validity with more recent Perls, or because they
are hard to duplicate.

... and there are also a lot of bugs that even not open, because nobody even
noticed them.

Just joking.

<!ENTITY Vadim REALLIFE "St.Petersburg, Russia">
&Vadim;

[p5pRT]

From @pjscott

At 02​:10 PM 3/10/01 -0500, Stephen P. Potter wrote​:

Lightning flashed, thunder crashed and Peter Scott <Peter@​PSDT.com> whispered​:
| http​://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/1999-11/msg00723.html
| is talking about something else, to be sure, but it demonstrates that the
| behavior you observed has been known about for some time. If it hasn't
| been changed since then it's probably not considered a bug.

*chuckle*
Just because it is an old bug doesn't necessarily mean it isn't a bug.
There are outstanding bugs in the database dating back to early '99, which
is when I believe we first started using the nugs database. Not that I'm
saying this is a bug, or isn't a bug. Just that age has nothing to do with
bugginess.

Shucks, you go and spoil a perfectly good attempt to promulgate the
infallibility of the P5P :-)

Anyway, the other thread I mentioned demonstrated that at the very least
there's insufficient agreement that this behavior constitutes a bug.

[p5pRT]

From [Unknown Contact. See original ticket]

There's a thread on the topic itself at
http​://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2000-05/msg00686.html

Fine enough, but then I claim that this is a bug​:

---

use strict;

sub fu {
  my $bar = 42 if (0); # Not declared, so​:
  $bar = 3; # Should warn​: Global symbol "$bar" requires explicit package name..
}

---

Dave++

---

Dave Ljung Madison http​://GetDave.com 415.922.2697
- If a tree falls in a forest, and there's nobody around, can I have it? --

[p5pRT]

From @tamias

On Mon, Mar 12, 2001 at 11​:01​:36AM -0800, David Madison wrote​:

There's a thread on the topic itself at
http​://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2000-05/msg00686.html

Fine enough, but then I claim that this is a bug​:

-------------------------
use strict;

sub fu {
my $bar = 42 if (0); # Not declared, so​:
$bar = 3; # Should warn​: Global symbol "$bar" requires explicit package name..

That is not correct. Please review the previous thread again.

$bar is declared at compile time, but is not reset at runtime.

Ronald

[p5pRT]

From [Unknown Contact. See original ticket]

On Fri, Mar 09, 2001 at 04​:39​:00PM -0800, Peter Scott wrote​:

This is well-known behavior and arguably not a bug. my() has compile-time
and run-time effects. Do a search for "Tom Christiansen" and "who says
Perl doesn't have statics?" and you may turn up a previous thread :-)

Is this actually documented anywhere? Or do we expected people to
read perl5-porters to know how their perl programs will behave?

Michael

[p5pRT]

From @simoncozens

On Tue, Mar 13, 2001 at 11​:41​:21AM +0000, Michael Stevens wrote​:

Is this actually documented anywhere? Or do we expected people to
read perl5-porters to know how their perl programs will behave?

We expect people not to do things that don't make sense, and not to be
surprised if they do.

[p5pRT]

From @Abigail

On Tue, Mar 13, 2001 at 12​:58​:47PM +0000, Simon Cozens wrote​:

On Tue, Mar 13, 2001 at 11​:41​:21AM +0000, Michael Stevens wrote​:

Is this actually documented anywhere? Or do we expected people to
read perl5-porters to know how their perl programs will behave?

We expect people not to do things that don't make sense, and not to be
surprised if they do.

I don't think it makes sense to tell people that what they did doesn't
make sense if they ask how/why it works and whether that's a bug or
intended behaviour.

It would be very nice if p5p (or the pumpking, or Larry (if he's around))
could at least acknowledge whether something is a bug or intended behaviour.

A "what you did doesn't make sense" is less than useful, and not very
Perlesque.

Abigail

[p5pRT]

From @jhi

On Tue, Mar 13, 2001 at 08​:11​:07PM +0100, abigail@​foad.org wrote​:

On Tue, Mar 13, 2001 at 12​:58​:47PM +0000, Simon Cozens wrote​:

On Tue, Mar 13, 2001 at 11​:41​:21AM +0000, Michael Stevens wrote​:

Is this actually documented anywhere? Or do we expected people to
read perl5-porters to know how their perl programs will behave?

We expect people not to do things that don't make sense, and not to be
surprised if they do.

I don't think it makes sense to tell people that what they did doesn't
make sense if they ask how/why it works and whether that's a bug or
intended behaviour.

It would be very nice if p5p (or the pumpking, or Larry (if he's around))
could at least acknowledge whether something is a bug or intended behaviour.

Well, I think "my ... if 0" is a bug. Well, not a bug as in
unexpected negative behaviour. It exhibits certain behaviour and some
people think it's positive behaviour. I think it's accidental and
shouldn't be depended on. If we want 'statics', let's have them by
design, not be accident.

A "what you did doesn't make sense" is less than useful, and not very
Perlesque.

Abigail

[p5pRT]

From @Abigail

On Tue, Mar 13, 2001 at 01​:13​:35PM -0600, Jarkko Hietaniemi wrote​:

On Tue, Mar 13, 2001 at 08​:11​:07PM +0100, abigail@​foad.org wrote​:

On Tue, Mar 13, 2001 at 12​:58​:47PM +0000, Simon Cozens wrote​:

On Tue, Mar 13, 2001 at 11​:41​:21AM +0000, Michael Stevens wrote​:

Is this actually documented anywhere? Or do we expected people to
read perl5-porters to know how their perl programs will behave?

We expect people not to do things that don't make sense, and not to be
surprised if they do.

I don't think it makes sense to tell people that what they did doesn't
make sense if they ask how/why it works and whether that's a bug or
intended behaviour.

It would be very nice if p5p (or the pumpking, or Larry (if he's around))
could at least acknowledge whether something is a bug or intended behaviour.

Well, I think "my ... if 0" is a bug. Well, not a bug as in
unexpected negative behaviour. It exhibits certain behaviour and some
people think it's positive behaviour. I think it's accidental and
shouldn't be depended on. If we want 'statics', let's have them by
design, not be accident.

Can I then suggest we officially declare this as deprecated and that
its behaviour might go away without notice in some future version of Perl?

Abigail

[p5pRT]

From @jhi

On Tue, Mar 13, 2001 at 08​:42​:05PM +0100, abigail@​foad.org wrote​:

On Tue, Mar 13, 2001 at 01​:13​:35PM -0600, Jarkko Hietaniemi wrote​:

On Tue, Mar 13, 2001 at 08​:11​:07PM +0100, abigail@​foad.org wrote​:

On Tue, Mar 13, 2001 at 12​:58​:47PM +0000, Simon Cozens wrote​:

On Tue, Mar 13, 2001 at 11​:41​:21AM +0000, Michael Stevens wrote​:

Is this actually documented anywhere? Or do we expected people to
read perl5-porters to know how their perl programs will behave?

We expect people not to do things that don't make sense, and not to be
surprised if they do.

I don't think it makes sense to tell people that what they did doesn't
make sense if they ask how/why it works and whether that's a bug or
intended behaviour.

It would be very nice if p5p (or the pumpking, or Larry (if he's around))
could at least acknowledge whether something is a bug or intended behaviour.

Well, I think "my ... if 0" is a bug. Well, not a bug as in
unexpected negative behaviour. It exhibits certain behaviour and some
people think it's positive behaviour. I think it's accidental and
shouldn't be depended on. If we want 'statics', let's have them by
design, not be accident.

Can I then suggest we officially declare this as deprecated and that
its behaviour might go away without notice in some future version of Perl?

I will integrate doc/parser-lexical-warning patches to that effect.