[P5P] [perl #34582] Array deref in return statement causes incorrect value in scalar context

# New Ticket Created by Rich Daley
# Please include the string: [perl #34582]
# in the subject line of all future correspondence about this issue.
# <URL: https://rt.perl.org/rt3/Ticket/Display.html?id=34582 >



This is a bug report for perl from [email protected],
generated with the help of perlbug 1.35 running under perl v5.8.4.


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

Dear all,

I have noticed that including an array deref in the return statement
of a sub causes unusual results when that sub is called in scalar
context.

Take the following script as an example:

--- start ---
#!/usr/bin/perl

use strict;
use warnings;
use English;
local $OFS = ' ';
local $ORS = "\n";

sub a {
my $foo = ['dick', 'harry'];
my @bar = ('tom', @$foo);
return @bar;
}

sub b {
my $foo = ['tom', 'dick', 'harry'];
return @$foo;
}

sub c {
my $foo = ['dick', 'harry'];
return ('tom', @$foo);
}

sub d {
my $foo = ['tom', 'dick'];
return (@$foo, 'harry');
}

print a;
print b;
print c;
print d;

print scalar a;
print scalar b;
print scalar c;
print scalar d;
--- end ---

The output is as follows:

--- start ---
tom dick harry
tom dick harry
tom dick harry
tom dick harry
3
3
2
harry
--- end ---

All four subs return the list ('tom', 'dick', 'harry') when called in
array context. However, only the first two return the value 3 (what I
would expect, the size of this array) when called in array context.

sub c, which returns a list containing a scalar and a deref'd array
ref, returns 2 instead of 3. I guessed this might be the compiler
noticing that two things are returned by c and optimising the return
into something like "return wantarray ? ('tom', @$foo) : 2", although
I doubt this is the behaviour most users would expect, since the list
returned in array context certainly has 3 elements. If this is the
intended behaviour, I would think that the warnings pragma should
generate a warning in this case.

sub d is even more interesting, since that evaluates to 'harry' in
scalar context. I don't know if this is intended, but again it seems
counter-intuitive to me, and it would, too, probably benefit from a
warning.

Thanks for listening!

~ Rich

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
category=core
severity=high
---
Site configuration information for perl v5.8.4:

Configured by Debian Project at Tue Mar 8 20:31:23 EST 2005.

Summary of my perl5 (revision 5 version 8 subversion 4) configuration:
Platform:
osname=linux, osvers=2.4.27-ti1211, archname=i386-linux-thread-multi
uname='linux kosh 2.4.27-ti1211 #1 sun sep 19 18:17:45 est 2004 i686 gnulinux '
config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=i386-linux -Dprefix=/usr -Dprivlib=/usr/share/perl/5.8 -Darchlib=/usr/lib/perl/5.8 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.8.4 -Dsitearch=/usr/local/lib/perl/5.8.4 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Uusesfio -Uusenm -Duseshrplib -Dlibperl=libperl.so.5.8.4 -Dd_dosuid -des'
hint=recommended, useposix=true, d_sigaction=define
usethreads=define use5005threads=undef useithreads=define usemultiplicity=define
useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
use64bitint=undef use64bitall=undef uselongdouble=undef
usemymalloc=n, bincompat5005=undef
Compiler:
cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN -fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
optimize='-O2',
cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN -fno-strict-aliasing -I/usr/local/include'
ccversion='', gccversion='3.3.5 (Debian 1:3.3.5-9)', gccosandvers=''
intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
alignbytes=4, prototype=define
Linker and Libraries:
ld='cc', ldflags =' -L/usr/local/lib'
libpth=/usr/local/lib /lib /usr/lib
libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
perllibs=-ldl -lm -lpthread -lc -lcrypt
libc=/lib/libc-2.3.2.so, so=so, useshrplib=true, libperl=libperl.so.5.8.4
gnulibc_version='2.3.2'
Dynamic Linking:
dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib'

Locally applied patches:


---
@INC for perl v5.8.4:
/etc/perl
/usr/local/lib/perl/5.8.4
/usr/local/share/perl/5.8.4
/usr/lib/perl5
/usr/share/perl5
/usr/lib/perl/5.8
/usr/share/perl/5.8
/usr/local/lib/site_perl
.

---
Environment for perl v5.8.4:
HOME=/home/rich
LANG=en_GB
LANGUAGE (unset)
LD_LIBRARY_PATH (unset)
LOGDIR (unset)
PATH=/home/rich/bin:/home/rich/bin:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games:/usr/lib/xscreensaver:/usr/games:/sbin:/usr/sbin:/usr/lib/xscreensaver:/usr/games:/sbin:/usr/sbin
PERL_BADLANG (unset)
SHELL=/bin/zsh