Blessed glob returned from function loses blessing

[p5pRT]

Migrated from rt.perl.org#1230 (status was 'resolved')

Searchable as RT1230$

[p5pRT]

From @mjdominus

I create a blessed glob in a function and return it to the caller.
The glob that the caller gets is a copy and is not blessed.

Demo program​:

-----------------BEGIN PROGRAM---------------------------------------------
my $z = mkglob();
print "2​: $z\n";
print "2​: ", ref(\$z), "\n";
print "2​: ", (\$z)->can('can'), "\n";

sub mkglob {
  my $glob = do {local *G};
  bless \$glob => 'Snonk!';
  print "1​: $glob\n";
  print "1​: ", ref(\$glob), "\n";
  print "1​: ", (\$glob)->can('can'), "\n";
  $glob;
}

-----------------END PROGRAM ---------------------------------------------

The `ref' call inside the function (labelled `1​:') yields `Snonk!'
because the glob is blessed. The ->can call succeeds, because \$glob
is a reference to a blessed glob.

However, the `ref' call outside the function (labelled `2​:') yields
`GLOB' because $z is not blessed, even though it should have been
copied from $glob. The `can' call aborts with a fatal error because
\$z is a reference to an unblessed object.

Using Devel​::Peek, you can see that the glob is actually copied on
return, and the blessing is not part of the data that is copied.

This behavior persists from at least 5.005_02 until at least 5.00557.

Perl Info

This perlbug was built using Perl 5.00502 - Sun Oct 18 04:25:09 CDT 1998
It is being executed now by  Perl 5.00556 - Wed May 19 22:26:34 EDT 1999.

Site configuration information for perl 5.00502:

Configured by root at Sun Oct 18 04:25:09 CDT 1998.

Summary of my perl5 (5.0 patchlevel 5 subversion 2) configuration:
  Platform:
    osname=linux, osvers=2.0.35, archname=i586-linux
    uname='linux darkstar 2.0.35 #10 tue oct 13 18:04:13 cdt 1998 i586 unknown '
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=undef useperlio=undef d_sfio=undef
  Compiler:
    cc='cc', optimize='-O2', gccversion=2.7.2.3
    cppflags='-Dbool=char -DHAS_BOOL -I/usr/local/include'
    ccflags ='-Dbool=char -DHAS_BOOL -I/usr/local/include'
    stdchar='char', d_stdstdio=define, usevfork=false
    intsize=4, longsize=4, ptrsize=4, doublesize=8
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    alignbytes=4, usemymalloc=n, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /shlib /lib /usr/lib
    libs=-lndbm -lgdbm -ldbm -ldb -ldl -lm -lc
    libc=/lib/libc.so.5.4.46, so=so, useshrplib=false, libperl=libperl.a
  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 5.00502:
    /usr/lib/perl5/5.00502/i586-linux
    /usr/lib/perl5/5.00502
    /usr/lib/perl5/site_perl/5.005/i586-linux
    /usr/lib/perl5/site_perl/5.005
    .


Environment for perl 5.00502:
    HOME=/home/mjd
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH=/lib:/usr/lib:/usr/X11R6/lib
    LOGDIR (unset)
    PATH=/home/mjd/bin:/usr/local/bin:/bin:/usr/bin:/usr/X11/bin:/usr/games:/sbin:/usr/sbin:/usr/local/bin/X11:/usr/local/bin/mh:/data/mysql/bin:/home/mjd/TPI/bin:/usr/local/mysql/bin
    PERL_BADLANG (unset)
    SHELL=/bin/bash

[p5pRT]

From @mjdominus

I create a blessed glob in a function and return it to the caller.
The glob that the caller gets is a copy and is not blessed.

The problem may be in the assignment operation, not the function
return value return. The following program illutrates the same
problem with no function call​:

  my $glob = *X;
  bless \$glob => 'Snonk!';
  print "1​: $glob\n";
  print "1​: ", ref(\$glob), "\n";
  print "1​: ", (\$glob)->can('can'), "\n";
  my $g2 = $glob;
  print "2​: $g2\n";
  print "2​: ", ref(\$g2), "\n";
  print "2​: ", (\$g2)->can('can'), "\n";

[p5pRT]

From @mjdominus

I create a blessed glob in a function and return it to the caller.
The glob that the caller gets is a copy and is not blessed.

The problem may be in the assignment operation, not the function
return value return. The following program illutrates the same
problem with no function call​:

  my $glob = *X;
  bless \$glob => 'Snonk!';
  print "1​: $glob\n";
  print "1​: ", ref(\$glob), "\n";
  print "1​: ", (\$glob)->can('can'), "\n";
  my $g2 = $glob;
  print "2​: $g2\n";
  print "2​: ", ref(\$g2), "\n";
  print "2​: ", (\$g2)->can('can'), "\n";

[p5pRT]

From @gbarr

But this is tru for any type, eg replace with

  my $scalar = "value"; bless \$scalar, ...
  my @​arr = (1); bless \@​arr, ...
  my %hash = (1,2); bless \%hash, ...

and you will see the same result. ie that the bless-ing is not
copied over.

On Wed, Aug 18, 1999 at 01​:27​:42PM -0400, Mark-Jason Dominus wrote​:

I create a blessed glob in a function and return it to the caller.
The glob that the caller gets is a copy and is not blessed.

The problem may be in the assignment operation, not the function
return value return. The following program illutrates the same
problem with no function call​:

my $glob = *X;
bless \$glob => 'Snonk!';
print "1​: $glob\n";
print "1​: ", ref(\$glob), "\n";
print "1​: ", (\$glob)->can('can'), "\n";
my $g2 = $glob;
print "2​: $g2\n";
print "2​: ", ref(\$g2), "\n";
print "2​: ", (\$g2)->can('can'), "\n";

--
Since you're clearly mad as a mongoose, I'll bid you good-day.
  -- Edmund to Captain Rum : Black Adder II "Potato"