${::foo} isn't handled correctly

[p5pRT]

Migrated from rt.perl.org#31797 (status was 'rejected')

Searchable as RT31797$

[p5pRT]

From matthew.harris@clearsightsystems.com

This is a bug report for perl from mharris@​litech.org,
generated with the help of perlbug 1.35 running under perl v5.8.5.

---

I can enclose a variable in braces to separate it from surrounding
text​:

  $ perl -we '$foo="hi"; print "${foo}\n"'
  hi

And I can use $​::foo to refer to a name in the 'main' package​:

  $ perl -we '$​::foo="hi"; print "$​::foo\n"'
  hi

But if I try to do both together, it produces the correct value but
warns me as if I didn't reference the variable at all​:

  $ perl -we '$​::foo="hi"; print "${​::foo}\n"'
  Name "main​::foo" used only once​: possible typo at -e line 1.
  hi
  $ perl -we '$​::foo="hi"; print "${main​::foo}\n"'
  hi

(The fact that I'm interpolating isn't important; dropping the double
quotes and the \n from the print statements gives the same results
without the newlines.)

FWIW, I don't know what $​::{foo} is supposed to do, but I wouldn't
have expected this result​:

  $ perl -we '$​::foo="hi"; print "$​::{foo}\n"'
  Name "main​::foo" used only once​: possible typo at -e line 1.
  *main​::foo

---

---

Flags​:
  category=core
  severity=low

---

Site configuration information for perl v5.8.5​:

Configured by Gentoo at Tue Sep 14 21​:33​:28 Local time zone must be
set--see zic manual page 2004.

Summary of my perl5 (revision 5 version 8 subversion 5) configuration​:
  Platform​:
  osname=linux, osvers=2.6.7-co-0.6.2, archname=i586-linux
  uname='linux colinux 2.6.7-co-0.6.2 #392 sat jul 10 19​:59​:22 idt
2004 i686 intel(r) pentium(r) 4 cpu 2.40ghz genuineintel gnulinux '
  config_args='-des -Darchname=i586-linux -Dcccdlflags=-fPIC
-Dccdlflags=-rdynamic -Dcc=gcc -Dprefix=/usr -Dvendorprefix=/usr
-Dsiteprefix=/usr -Dlocincpth= -Doptimize=-march=i586 -funroll-loops
-Duselargefiles -Dd_dosuid -Dd_semctl_semun -Dscriptdir=/usr/bin
-Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3
-Dinstallman1dir=/usr/share/man/man1
-Dinstallman3dir=/var/tmp/portage/perl-5.8.5/image//usr/share/man/man3
-Dman1ext=1 -Dman3ext=3pm -Dcf_by=Gentoo -Ud_csh -Ui_ndbm -Ui_gdbm
-Ui_db'
  hint=recommended, useposix=true, d_sigaction=define
  usethreads=undef use5005threads=undef useithreads=undef
usemultiplicity=undef
  useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
  use64bitint=undef use64bitall=undef uselongdouble=undef
  usemymalloc=n, bincompat5005=undef
  Compiler​:
  cc='gcc', ccflags ='-fno-strict-aliasing -pipe -D_LARGEFILE_SOURCE
-D_FILE_OFFSET_BITS=64',
  optimize='-march=i586 -funroll-loops',
  cppflags='-DPERL5 -fno-strict-aliasing -pipe'
  ccversion='', gccversion='3.3.4 20040623 (Gentoo Linux 3.3.4-r1,
ssp-3.3.2-2, pie-8.7.6)', 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=-lpthread -lnsl -lndbm -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc
  perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
  libc=/lib/libc-2.3.4.so, so=so, useshrplib=false, libperl=libperl.a
  gnulibc_version='2.3.4'
  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 v5.8.5​:
  /etc/perl
  /usr/lib/perl5/site_perl/5.8.5/i586-linux
  /usr/lib/perl5/site_perl/5.8.5
  /usr/lib/perl5/site_perl/5.8.4/i586-linux
  /usr/lib/perl5/site_perl/5.8.4
  /usr/lib/perl5/site_perl/5.8.3/i586-linux
  /usr/lib/perl5/site_perl/5.8.3
  /usr/lib/perl5/site_perl/5.8.2/i586-linux
  /usr/lib/perl5/site_perl/5.8.2
  /usr/lib/perl5/site_perl/5.8.0
  /usr/lib/perl5/site_perl
  /usr/lib/perl5/vendor_perl/5.8.5/i586-linux
  /usr/lib/perl5/vendor_perl/5.8.5
  /usr/lib/perl5/vendor_perl/5.8.3/i586-linux
  /usr/lib/perl5/vendor_perl/5.8.3
  /usr/lib/perl5/vendor_perl/5.8.2/i586-linux
  /usr/lib/perl5/vendor_perl/5.8.2
  /usr/lib/perl5/vendor_perl
  /usr/lib/perl5/5.8.5/i586-linux
  /usr/lib/perl5/5.8.5
  /usr/local/lib/site_perl
  /usr/lib/perl5/site_perl/5.8.4/i586-linux
  /usr/lib/perl5/site_perl/5.8.4
  /usr/lib/perl5/site_perl/5.8.3/i586-linux
  /usr/lib/perl5/site_perl/5.8.3
  /usr/lib/perl5/site_perl/5.8.2/i586-linux
  /usr/lib/perl5/site_perl/5.8.2
  /usr/lib/perl5/site_perl/5.8.0
  .

---

Environment for perl v5.8.5​:
  HOME=/home/mharris
  LANG (unset)
  LANGUAGE (unset)
  LD_LIBRARY_PATH (unset)
  LOGDIR (unset)

PATH=/bin​:/usr/bin​:/usr/local/bin​:/opt/bin​:/usr/i586-pc-linux-gnu/gcc-bi
n/3.4​:/usr/X11R6/bin​:/opt/blackdown-jdk-1.4.2_rc1/bin​:/opt/blackdown-jdk
-1.4.2_rc1/jre/bin
  PERL_BADLANG (unset)
  SHELL=/bin/bash

[p5pRT]

From @rgs

Matthew Harris wrote​:

I can enclose a variable in braces to separate it from surrounding
text​:

$ perl -we '$foo="hi"; print "${foo}\n"'
hi

And I can use $​::foo to refer to a name in the 'main' package​:

$ perl -we '$​::foo="hi"; print "$​::foo\n"'
hi

But if I try to do both together, it produces the correct value but
warns me as if I didn't reference the variable at all​:

$ perl -we '$​::foo="hi"; print "${​::foo}\n"'
Name "main​::foo" used only once​: possible typo at -e line 1.
hi

Here, the second statement tries to look up a variable whose name
is "​::foo", not "foo".

FWIW, I don't know what $​::{foo} is supposed to do, but I wouldn't
have expected this result​:

It's simply a hash lookup in %​:: (a.k.a. the symbol table, documented
in the perlmod manpage.)

[p5pRT]

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

[p5pRT]

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

[p5pRT]

From matthew.harris@clearsightsystems.com

Thanks for your quick response.

Rafael Garcia-Suarez wrote​:

Matthew Harris wrote​:

$ perl -we '$​::foo="hi"; print "${​::foo}\n"'
Name "main​::foo" used only once​: possible typo at -e line 1.
hi

Here, the second statement tries to look up a variable whose
name is "​::foo", not "foo".

Then why does it still print "hi"? Is it normal for Perl to try to look
up more than one variant of a variable name?

Even if this is what it's doing, is this correct behavior? My reasoning
is this​: ${main​::foo} evaluates to $main​::foo, and according to the
first paragraph of perlmod the "main" can always be omitted, so ${​::foo}
should be identical. Can you point me to a source (e.g., somewhere in
the Perl documentation, or an instance of DWIM) that explains the
observed behavior?

[p5pRT]

From nick@ing-simmons.net

Matthew Harris <matthew.harris@​clearsightsystems.com> writes​:

Thanks for your quick response.

Rafael Garcia-Suarez wrote​:

Matthew Harris wrote​:

$ perl -we '$​::foo="hi"; print "${​::foo}\n"'
Name "main​::foo" used only once​: possible typo at -e line 1.
hi

Here, the second statement tries to look up a variable whose
name is "​::foo", not "foo".

Then why does it still print "hi"? Is it normal for Perl to try to look
up more than one variant of a variable name?

nick@​llama​:/home/p4work/TI/RTLGen> perl -we 'use strict; $​::foo="hi"; print "${​::foo}\n"'
Bareword "​::foo" not allowed while "strict subs" in use at -e line 1.

${​::foo} is a symbolic reference and resolves to $main​::foo at run time.
The "used only once" is reported at end of compile phase
when it _has_ only been used once.

Even if this is what it's doing, is this correct behavior? My reasoning
is this​: ${main​::foo} evaluates to $main​::foo, and according to the
first paragraph of perlmod the "main" can always be omitted, so ${​::foo}
should be identical. Can you point me to a source (e.g., somewhere in
the Perl documentation, or an instance of DWIM) that explains the
observed behavior?

[p5pRT]

From @davidnicol

nick@​llama​:/home/p4work/TI/RTLGen> perl -we 'use strict; $​::foo="hi"; print "${​::foo}\n"'
Bareword "​::foo" not allowed while "strict subs" in use at -e line 1.

${​::foo} is a symbolic reference and resolves to $main​::foo at run time.
The "used only once" is reported at end of compile phase
when it _has_ only been used once.

:​:foo is a static expression known at compile time, why isn't it optimized?

--
David L Nicol
"Valuable ideas can withstand scrutiny" -- authors of /XP Explained/

[p5pRT]

From nick@ing-simmons.net

David Nicol <davidnicol@​gmail.com> writes​:

nick@​llama​:/home/p4work/TI/RTLGen> perl -we 'use strict; $​::foo="hi"; print "${​::foo}\n"'
Bareword "​::foo" not allowed while "strict subs" in use at -e line 1.

${​::foo} is a symbolic reference and resolves to $main​::foo at run time.
The "used only once" is reported at end of compile phase
when it _has_ only been used once.

​::foo is a static expression known at compile time, why isn't it optimized?

I was reporting what happens not why ;-)

Doesn't alter the fact that ${"main​::foo"} is a symbolic ref
and needs to bind to any re-assigns to the glob that occur.