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[perl #123721] Dumper loses blessedness from unreferenced scalars

From:
Zefram
Date:
February 3, 2015 11:32
Subject:
[perl #123721] Dumper loses blessedness from unreferenced scalars
Message ID:
rt-4.0.18-22544-1422963115-1340.123721-75-0@perl.org
# New Ticket Created by  Zefram 
# Please include the string:  [perl #123721]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=123721 >



This is a bug report for perl from zefram@fysh.org,
generated with the help of perlbug 1.39 running under perl 5.18.2.


-----------------------------------------------------------------
[Please describe your issue here]

$ perl -MData::Dumper=Dumper -we '@a=(3); bless \$a[0], "Foo"; print Dumper \$a[0]; print Dumper \@a'
$VAR1 = bless( do{\(my $o = 3)}, 'Foo' );
$VAR1 = [
          3
        ];

Dumper is willing to show the blessedness of a scalar that it encounters
through a reference, but fails to show it if it encounters the scalar
as an array element.  (Likewise a hash element.)

Due to Dumper displaying aliasing, it *can* end up representing the
blessedness of an array element, except that it actually screws up with
the aliasing expression.  Whether the blessedness is represented depends
on the order in which parts of a data structure are encountered:

$ perl -MData::Dumper=Dumper -we '@a=(3,0); $a[1] = \$a[0]; bless \$a[0], "Foo"; print Dumper \@a'
$VAR1 = [
          3,
          \$VAR1->[0]
        ];

Blessed scalar comes before reference: the blessing is not preserved,
but the aliasing is correct.

$ perl -MData::Dumper=Dumper -we '@a=(0,3); $a[0] = \$a[1]; bless \$a[1], "Foo"; print Dumper \@a'
$VAR1 = [
          bless( do{\(my $o = 3)}, 'Foo' ),
          ${$VAR1->[0]}
        ];

Reference comes before blessed scalar: the blessing is preserved, but
the expression used for the aliasing doesn't account for the copying
performed by the [...] array constructor.

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=library
    severity=low
    module=Data::Dumper
---
Site configuration information for perl 5.18.2:

Configured by root at Wed Mar 26 14:32:51 UTC 2014.

Summary of my perl5 (revision 5 version 18 subversion 2) configuration:
   
  Platform:
    osname=linux, osvers=3.2.0-4-amd64, archname=x86_64-linux-ld
    uname='linux ukmcwzefram.photobox.priv 3.2.0-4-amd64 #1 smp debian 3.2.54-2 x86_64 gnulinux '
    config_args='-des -Duseshrplib -Duse64bitint -Duselongdouble -Uusethreads -Uusemultiplicity -Dprefix=/opt/perl-5.18.2 -Dsiteprefix=/opt/perl-5.18.2 -Dvendorprefix=/opt/perl-5.18.2/vendor -Doptimize=-ggdb -O3 -fbranch-target-load-optimize -fgcse-las -fgcse-sm -fipa-pta -floop-block -floop-interchange -floop-strip-mine -fmodulo-sched -fomit-frame-pointer -freorder-blocks-and-partition -fsched-spec-load -fsched-spec-load-dangerous -ftree-loop-distribution -Dcccdlflags=-fPIC -O3 -pipe'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=define, use64bitall=define, uselongdouble=define
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-ggdb -O3 -fbranch-target-load-optimize -fgcse-las -fgcse-sm -fipa-pta -floop-block -floop-interchange -floop-strip-mine -fmodulo-sched -fomit-frame-pointer -freorder-blocks-and-partition -fsched-spec-load -fsched-spec-load-dangerous -ftree-loop-distribution',
    cppflags='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.7.2', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
    ivtype='long', ivsize=8, nvtype='long double', nvsize=16, Off_t='off_t', lseeksize=8
    alignbytes=16, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib /usr/lib
    libs=-lnsl -ldb -ldl -lm -lcrypt -lutil -lc
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lc
    libc=, so=so, useshrplib=true, libperl=libperl.so
    gnulibc_version='2.17'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E -Wl,-rpath,/opt/perl-5.18.2/lib/5.18.2/x86_64-linux-ld/CORE'
    cccdlflags='-fPIC -O3 -pipe', lddlflags='-shared -ggdb -O3 -fbranch-target-load-optimize -fgcse-las -fgcse-sm -fipa-pta -floop-block -floop-interchange -floop-strip-mine -fmodulo-sched -fomit-frame-pointer -freorder-blocks-and-partition -fsched-spec-load -fsched-spec-load-dangerous -ftree-loop-distribution -L/usr/local/lib -fstack-protector'

Locally applied patches:
    

---
@INC for perl 5.18.2:
    /opt/perl-5.18.2/lib/site_perl/5.18.2/x86_64-linux-ld
    /opt/perl-5.18.2/lib/site_perl/5.18.2
    /opt/perl-5.18.2/vendor/lib/vendor_perl/5.18.2/x86_64-linux-ld
    /opt/perl-5.18.2/vendor/lib/vendor_perl/5.18.2
    /opt/perl-5.18.2/lib/5.18.2/x86_64-linux-ld
    /opt/perl-5.18.2/lib/5.18.2
    .

---
Environment for perl 5.18.2:
    HOME=/home/zefram
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/zefram/pub/x86_64-unknown-linux-gnu/bin:/home/zefram/pub/common/bin:/usr/bin:/bin:/usr/local/bin:/usr/games:/opt/babelhttpd-2.2.26/bin:/opt/babelhttpd-2.4.7/bin:/opt/geoip/bin:/opt/httpd/bin:/opt/perl/bin
    PERL_BADLANG (unset)
    SHELL=/usr/bin/zsh




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