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[perl #59884] 'x' forces scalar context on array variables

From: James Schneider (via RT) <perlbug-followup@perl.org>
Reply-To: perl5-porters@perl.org
To: bugs-bitbucket@netlabs.develooper.com
Date: Mon, 13 Oct 2008 14:11:39 -0700
Message-ID: <rt-3.6.HEAD-11699-1223932298-1364.59884-75-0@perl.org>
# New Ticket Created by  James Schneider 
# Please include the string:  [perl #59884]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=59884 >


This is a bug report for perl from jschneid@redhat.com,

generated with the help of perlbug 1.35 running under perl v5.8.8.


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

The 'x' operator forces scalar context on the left operand, unless
that operand is enclosed in parens, even if the left operand is an
array variable.

For example, the following code fragment prints the string "22", rather
than the expected four lines of alternating words:

@foo = qw(foo bar);
print "$_\n" foreach @foo x 2;

The alternative:

print "$_\n" foreach qw(foo bar) x 2;

does print the alternating lines.

"perldoc perlop" is not clear on the expected behavior - quoting:

  In scalar context or if the left operand is not enclosed in parentheses,
  it returns a string consisting of the left operand repeated the number of
  times specified by the right operand.  In list context, if the left operand
  is enclosed in parentheses or is a list formed by "qw/STRING/", it repeats
  the list.

It could be read that the behavior is the documented behavior, but it
certainly looks like wrong behavior.  It also violates the principal of
least surprise.  Why should the "x" operator force a particular context
on an operand that already has a perfectly good context of its own?

In the event this is not fixed, I suggest the passage above be amended to:

  The "x" operator will evaluate its left operand in scalar context,
  unless the left operand is enclosed in parentheses, or is a list formed
  by "qw/STRING/", where it will be evaluated in list context.  In scalar
  context, it returns a string consisting of the left operand repeated
  the number of times specified by the right operand.  In list context,
  it repeats the list.

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=wishlist
---
This perlbug was built using Perl v5.8.8 in the Red Hat build system.
It is being executed now by Perl v5.8.8 - Tue Oct 23 12:21:05 EDT 2007.

Site configuration information for perl v5.8.8:

Configured by Red Hat, Inc. at Tue Oct 23 12:21:05 EDT 2007.

Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
  Platform:
    osname=linux, osvers=2.6.9-55.0.9.elsmp, archname=i386-linux-thread-multi
    uname='linux hs20-bc1-6.build.redhat.com 2.6.9-55.0.9.elsmp #1 smp tue sep 25 02:16:15 edt 2007 i686 i686 i386 gnulinux '
    config_args='-des -Doptimize=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables -Dversion=5.8.8 -Dmyhostname=localhost -Dperladmin=root@localhost -Dcc=gcc -Dcf_by=Red Hat, Inc. -Dinstallprefix=/usr -Dprefix=/usr -Darchname=i386-linux -Dvendorprefix=/usr -Dsiteprefix=/usr -Duseshrplib -Dusethreads -Duseithreads -Duselargefiles -Dd_dosuid -Dd_semctl_semun -Di_db -Ui_ndbm -Di_gdbm -Di_shadow -Di_syslog -Dman3ext=3pm -Duseperlio -Dinstallusrbinperl=n -Ubincompat5005 -Uversiononly -Dpager=/usr/bin/less -isr -Dd_gethostent_r_proto -Ud_endhostent_r_proto -Ud_sethostent_r_proto -Ud_endprotoent_r_proto -Ud_setprotoent_r_proto -Ud_endservent_r_proto -Ud_setservent_r_proto -Dinc_version_list=5.8.7 5.8.6 5.8.5 -Dscriptdir=/usr/bin'
    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='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -Wdeclaration-after-statement -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -I/usr/include/gdbm',
    optimize='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -Wdeclaration-after-statement -I/usr/local/include -I/usr/include/gdbm'
    ccversion='', gccversion='4.1.1 20070105 (Red Hat 4.1.1-52)', 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='gcc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lresolv -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lpthread -lc
    perllibs=-lresolv -lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    libc=/lib/libc-2.5.so, so=so, useshrplib=true, libperl=libperl.so
    gnulibc_version='2.5'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E -Wl,-rpath,/usr/lib/perl5/5.8.8/i386-linux-thread-multi/CORE'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables -L/usr/local/lib'

Locally applied patches:
    

---
@INC for perl v5.8.8:
    /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.7/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.6/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.5/i386-linux-thread-multi
    /usr/lib/perl5/site_perl/5.8.8
    /usr/lib/perl5/site_perl/5.8.7
    /usr/lib/perl5/site_perl/5.8.6
    /usr/lib/perl5/site_perl/5.8.5
    /usr/lib/perl5/site_perl
    /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.7/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.6/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.5/i386-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.8.8
    /usr/lib/perl5/vendor_perl/5.8.7
    /usr/lib/perl5/vendor_perl/5.8.6
    /usr/lib/perl5/vendor_perl/5.8.5
    /usr/lib/perl5/vendor_perl
    /usr/lib/perl5/5.8.8/i386-linux-thread-multi
    /usr/lib/perl5/5.8.8
    .

---
Environment for perl v5.8.8:
    HOME=/home/jschneid
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/usr/lib/qt-3.3/bin:/usr/kerberos/bin:/usr/local/bin:/bin:/usr/bin:/sbin:/home/jschneid/bin
    PERL_BADLANG (unset)
    SHELL=/bin/bash
Follow-Ups from:: Michael G Schwern <schwern@pobox.com>
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