Warning about scalar @a[$b] triggered in list context

[p5pRT]

Migrated from rt.perl.org#32083 (status was 'open')

Searchable as RT32083$

[p5pRT]

From @chipdude

Created by chip@pobox.com

The warning about @​a[$b] being better written as $a[$b] is triggering
even in list context, which is wrong.

  $ perl -wle 'my ($a) = @​ARGV[0]'
  Scalar value @​ARGV[0] better written as $ARGV[0] at -e line 1.

It's quite plausible to have a one-element array slice if you're
planning on extending the slice later. Consider a POE sub arg list​:

  sub state {
  my ($self) = @​_[OBJECT];
  # ...
  }

You wouldn't want to make that a $, because if you added another
subscript, the slice would silently fail​:

  sub state {
  my ($self, $arg) = $_[OBJECT, ARG0]; # OOPS BUG HERE
  # ...
  }

Perl Info

Flags:
    category=core
    severity=low

Site configuration information for perl v5.8.4:

Configured by Debian Project at Sun Sep 26 12:11:30 CEST 2004.

Summary of my perl5 (revision 5 version 8 subversion 4) configuration:
  Platform:
    osname=linux, osvers=2.6.8-1-686, archname=i386-linux-thread-multi
    uname='linux cachaca 2.6.8-1-686 #1 sat aug 28 14:11:39 edt 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='3.3.4 (Debian 1:3.3.4-12)', 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
    /usr/local/share/perl/5.8.3
    /usr/local/share/perl/5.8.2
    /usr/local/share/perl/5.8.1
    /usr/local/share/perl/5.8.0
    .


Environment for perl v5.8.4:
    HOME=/u/home/chip
    LANG (unset)
    LANGUAGE (unset)
    LC_CTYPE=en_US.ISO-8859-1
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/u/home/chip/bin:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games
    PERL_BADLANG (unset)
    SHELL=/bin/zsh

[p5pRT]

From @xdg

Still exists on 5.11.1

[p5pRT]

The RT System itself - Status changed from 'new' to 'open'

[p5pRT]

From @cpansprout

On Thu Oct 21 19​:16​:41 2004, chip wrote​:

The warning about @​a[$b] being better written as $a[$b] is triggering
even in list context, which is wrong.

$ perl \-wle 'my \($a\) = @​ARGV\[0\]'
Scalar value @​ARGV\[0\] better written as $ARGV\[0\] at \-e line 1\.

It's quite plausible to have a one-element array slice if you're
planning on extending the slice later. Consider a POE sub arg list​:

sub state \{
    my \($self\) = @​\_\[OBJECT\];
    \# \.\.\.
\}

You wouldn't want to make that a $, because if you added another
subscript, the slice would silently fail​:

sub state \{
    my \($self\, $arg\) = $\_\[OBJECT\, ARG0\];   \# OOPS BUG HERE
    \# \.\.\.
\}

This is one of my pet peeves. It’s the bareword it shouldn’t be warning
about. Whether it should warn for @​_[0] in list context is slightly
more debatable.

--

Father Chrysostomos