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wantarray fails in END, INIT, and CHECK blocks #1418

Closed p5pRT closed 19 years ago

p5pRT commented 24 years ago

Migrated from rt.perl.org#2562 (status was 'resolved')

Searchable as RT2562$

p5pRT commented 24 years ago

From khw@bighorn.dr.lucent.com

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

# wantarray in the END block returns true in void context instead of the proper 'undefined'. This program illustrates​:

use strict;

sub fails($) {   my $string = shift;   print $string\, "\, not void context\n" if defined wantarray;   print $string\, "\, in void context\n" unless defined wantarray; }

fails("not in END"); # void context

END {   fails("in END"); # void context }

# both calls to 'fails' should print the same result\, but they don't # on my system. And by the way\, the O'Reilly "Programming Perl" p. 241 # 2nd edition fails to mention wantarray being undefined in void context # It's in perlpod perlfunc.

Site configuration information for perl 5.00503​:

Configured by expmake at Fri Sep 10 16​:33​:51 CDT 1999.

Summary of my perl5 (5.0 patchlevel 5 subversion 3) configuration​:   Platform​:   osname=solaris\, osvers=2.4\, archname=sun4-solaris   uname='sunos nwpep 5.4 generic_101945-61 sun4d sparc '   hint=recommended\, useposix=true\, d_sigaction=define   usethreads=undef useperlio=undef d_sfio=undef   Compiler​:   cc='cc'\, optimize='-O'\, gccversion=   cppflags=''   ccflags =''   stdchar='unsigned char'\, d_stdstdio=define\, usevfork=false   intsize=4\, longsize=4\, ptrsize=4\, doublesize=8   d_longlong=define\, longlongsize=8\, d_longdbl=define\, longdblsize=16   alignbytes=8\, usemymalloc=y\, prototype=define   Linker and Libraries​:   ld='cc'\, ldflags =''   libpth=/lib /usr/lib /usr/ccs/lib   libs=-lsocket -lnsl -ldl -lm -lc -lcrypt   libc=/lib/libc.so\, so=so\, useshrplib=false\, libperl=libperl.a   Dynamic Linking​:   dlsrc=dl_dlopen.xs\, dlext=so\, d_dlsymun=undef\, ccdlflags=' '   cccdlflags='-KPIC'\, lddlflags='-G'

Locally applied patches​:  

@​INC for perl 5.00503​:   /opt/exp/perl/lib/5.00503/sun4-solaris   /opt/exp/perl/lib/5.00503   /opt/exp/perl/lib/site_perl/5.005/sun4-solaris   /opt/exp/perl/lib/site_perl/5.005   .

Environment for perl 5.00503​:   HOME=/home/khw   LANG (unset)   LANGUAGE (unset)   LD_LIBRARY_PATH=/usr/openwin/lib​:/usr/lib   LOGDIR (unset)   PATH=/usr/local/src/post/src/post​:/home/khw/specbin​:/home/khw/bin​:/home/khw/print/bin​:/usr/add-on/dwb/bin​:/usr/5bin​:/usr/ucb​:/usr/add-on/local/bin​:/usr/add-on/unison/bin​:/opt/exp/bin​:/usr/sbin​:/usr/add-on/zmail/bin​:/usr/add-on/ncmp/630/bin​:/usr/add-on/SUNWspro/bin​:/usr/openwin/bin​:/usr/openwin/demo​:/usr/bin/X11​:/usr/add-on/ncmp/bin​:/usr/ccs/bin​:/etc​:/usr/add-on/defty5/bin​:/usr/add-on/tools/bin​:/opt/exp/perl/bin​:   PERL_BADLANG (unset)   SHELL=/bin/ksh

p5pRT commented 24 years ago

From [Unknown Contact. See original ticket]

khw@​bighorn.dr.lucent.com wrote​:

generated with the help of perlbug 1.26 running under perl 5.00503. ----------------------------------------------------------------- # wantarray in the END block returns true in void context instead of the proper 'undefined'. This program illustrates​:

This is still true in RC3. It's apparently only true for the last statement in the END block\, though.

p5pRT commented 24 years ago

From @tamias

On Wed\, Mar 22\, 2000 at 10​:29​:33AM -0500\, Norton Allen wrote​:

khw@​bighorn.dr.lucent.com wrote​:

generated with the help of perlbug 1.26 running under perl 5.00503. ----------------------------------------------------------------- # wantarray in the END block returns true in void context instead of the proper 'undefined'. This program illustrates​:

This is still true in RC3. It's apparently only true for the last statement in the END block\, though.

Clearly\, the END block itself is not being called in void context.

Ronald

p5pRT commented 24 years ago

From [Unknown Contact. See original ticket]

Ronald J Kimball wrote​:

On Wed\, Mar 22\, 2000 at 10​:29​:33AM -0500\, Norton Allen wrote​:

khw@​bighorn.dr.lucent.com wrote​:

generated with the help of perlbug 1.26 running under perl 5.00503. ----------------------------------------------------------------- # wantarray in the END block returns true in void context instead of the proper 'undefined'. This program illustrates​:

This is still true in RC3. It's apparently only true for the last statement in the END block\, though.

Clearly\, the END block itself is not being called in void context.

  Of course\, it appears to be called in scalar context.  

p5pRT commented 22 years ago

From @floatingatoll

[khw@​bighorn.dr.lucent.com - Tue Mar 21 08​:54​:01 2000]​:

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

# wantarray in the END block returns true in void context instead of the proper 'undefined'. This program illustrates​:

use strict;

sub fails($) { my $string = shift; print $string\, "\, not void context\n" if defined wantarray; print $string\, "\, in void context\n" unless defined wantarray; }

fails("not in END"); # void context

END { fails("in END"); # void context }

# both calls to 'fails' should print the same result\, but they don't # on my system. And by the way\, the O'Reilly "Programming Perl" p. 241 # 2nd edition fails to mention wantarray being undefined in void context # It's in perlpod perlfunc.

Confirmed to fail against @​17821 (5.8/5.9 development track).

p5pRT commented 21 years ago

From @schwern

[coral - Sun Sep 1 16​:17​:31 2002]​:

Still exists in 5.8.1 RC2

p5pRT commented 19 years ago

From @smpeters

[schwern - Tue Jul 15 19​:50​:14 2003]​:

[coral - Sun Sep 1 16​:17​:31 2002]​:

Still exists in 5.8.1 RC2

Rather than reconfirm the existance of this bug\, I thought I'd investigate a bit further. It does\, in fact\, continue to exist in today's blead. My investigations found that wantarry has issues in INIT and CHECK as well as END. I modified the bug title to clarify this. Also\, using Devel​::Peek\, I was able to confirm that wantarray() returns a different value in a void context inside of END\, INIT\, and CHECK than outside. In END\, INIT\, and CHECK\, wantarry returns a PVNV. Outside those functions\, it returns NULL. See the example program below for examples and output.

cat ~/sandbox/perl_rt/rt_2562.pl use Devel​::Peek 'Dump';

sub foo {   fails("in foo()"); # void context }

sub fails($) {   my $string = $_[0];   print $string\, "\, not void context\n" if defined wantarray;   print $string\, "\, in void context\n" if ! defined wantarray;   print ref wantarray; print "\n"; }

fails("not in END"); # void context foo();

eval {   fails("in eval"); };

Dump(wantarray());

INIT {   fails("in INIT"); }

CHECK {   fails("in CHECK"); }

END {   Dump(wantarray());   fails("in END"); # void context }

./perl -Ilib ~/sandbox/perl_rt/rt_2562.pl in CHECK\, not void context

in INIT\, not void context

not in END\, in void context

in foo()\, in void context

in eval\, in void context

SV = NULL(0x0) at 0x3c030640   REFCNT = 2147483617   FLAGS = (READONLY)

SV = PVNV(0x3c03141c) at 0x3c03064c   REFCNT = 2147483647   FLAGS = (IOK\,NOK\,POK\,READONLY\,pIOK\,pNOK\,pPOK)   IV = 0   NV = 0   PV = 0x3c02b040 ""\0   CUR = 0   LEN = 1 in END\, not void context

p5pRT commented 19 years ago

From mjtg@cam.ac.uk

Steve Peters wrote

In END\, INIT\, and CHECK\, wantarry returns a PVNV. Outside those functions\, it returns NULL.

Those values are just the standard builtin values of 'true'\, 'false' and 'undef'\, i.e. PL_sv_yes\, PL_sv_no and PL_sv_undef.

I haven't looked at the original bug but I assume it is making some some comment about the values of wantarray() in END{}. But this is a pretty stupid thing to worry about. The answer is to document it as not being specified\, as in the attached patch.

Mike Guy

Inline Patch ```diff --- ./pod/perlfunc.pod.orig 2003-07-27 22:47:22.000000000 +0100 +++ ./pod/perlfunc.pod 2004-12-10 18:56:58.051871000 +0000 @@ -6530,15 +6530,19 @@ =item wantarray -Returns true if the context of the currently executing subroutine is -looking for a list value. Returns false if the context is looking -for a scalar. Returns the undefined value if the context is looking -for no value (void context). +Returns true if the context of the currently executing subroutine or +C is looking for a list value. Returns false if the context is +looking for a scalar. Returns the undefined value if the context is +looking for no value (void context). return unless defined wantarray; # don't bother doing more my @a = complex_calculation(); return wantarray ? @a : "@a"; +C's result is unspecified in the top level of a file, +in a C, C, C or C block, or in a C +method. + This function should have been named wantlist() instead. =item warn LIST End of patch ```
p5pRT commented 19 years ago

From @rgs

Mike Guy wrote in perl.perl5.porters :

Those values are just the standard builtin values of 'true'\, 'false' and 'undef'\, i.e. PL_sv_yes\, PL_sv_no and PL_sv_undef.

I haven't looked at the original bug but I assume it is making some some comment about the values of wantarray() in END{}. But this is a pretty stupid thing to worry about. The answer is to document it as not being specified\, as in the attached patch.

--- ./pod/perlfunc.pod.orig 2003-07-27 22​:47​:22.000000000 +0100 +++ ./pod/perlfunc.pod 2004-12-10 18​:56​:58.051871000 +0000

Thanks\, applied as #23639.

p5pRT commented 19 years ago

@smpeters - Status changed from 'open' to 'resolved'