in reply to Re^3: A Scalar::Util::refaddr Oddity
in thread A Scalar::Util::refaddr Oddity

Because that idiom fails if $object overloads addition to do something else.

Doh! (Can you tell I don't mess with overloading much? Wasn't even on my radar screen.) OK, then, quick perusal of overload reveals the StrVal function, which can get us back to the original "grab the right substring and convert" approach without the reblessing. 

use strict;
use warnings;
use Scalar::Util qw( refaddr );

package Foo;
use overload
    '0+'    => sub { 0 },
    q{""}   => sub { "Some Object" },
    fallback => 1;

package main;
use overload;

sub refaddr_pp {
    return if not ref $_[0];
    overload::StrVal($_[0]) =~ /0x(\w+)/;
    return hex $1;
}

my $obj = bless {}, 'Foo';
my $ref = {};

print 'stringify  $obj: ', "$obj",           "\n";
print 'refaddr    $obj: ', refaddr($obj),    "\n";
print 'refaddr_pp $obj: ', refaddr_pp($obj), "\n\n";
print 'stringify  $ref: ', "$ref",           "\n";
print 'refaddr    $ref: ', refaddr($ref),    "\n";
print 'refaddr_pp $ref: ', refaddr_pp($ref),    "\n\n";

[download]

Prints

stringify  $obj: Some Object
refaddr    $obj: 155892768
refaddr_pp $obj: 155892768

stringify  $ref: HASH(0x94abd10)
refaddr    $ref: 155893008
refaddr_pp $ref: 155893008

[download]

-xdg

Code written by xdg and posted on PerlMonks is public domain. It is provided as is with no warranties, express or implied, of any kind. Posted code may not have been tested. Use of posted code is at your own risk.

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Re^5: A Scalar::Util::refaddr Oddity
by adrianh (Chancellor) on Sep 26, 2005 at 16:04 UTC

    That would work - but pulling in overload seems overkill when we can just use Scalar::Util::blessed to see whether the reblessing hack is necessary.

[reply]

      You're the benchmark master. ;-) One-time hit to require overload and then a single function call, or always check blessed, store the original package and bless twice?

      Or how about this -- so we only use it if something else has loaded overload and the object is actually overloaded?

      sub refaddr_pp {
    return if not ref $_[0];
    if (    exists $INC{'overload.pm'}  
         && overload::Overloaded($_[0]) ) {
        overload::StrVal($_[0]) =~ /0x(\w+)/;
        return hex $1;
    }
    else {
        return 0 + $_[0];
    }
}

      [download]

      -xdg

      Code written by xdg and posted on PerlMonks is public domain. It is provided as is with no warranties, express or implied, of any kind. Posted code may not have been tested. Use of posted code is at your own risk.

[reply]
[d/l]
        You're the benchmark master. ;-) One-time hit to require overload and then a single function call, or always check blessed, store the original package and bless twice?

        No idea :-) I was thinking of memory footprint rather than speed myself... but you're right. Capital mistake to theorise ahead of data and all that.

[reply]
Re^5: A Scalar::Util::refaddr Oddity
by hv (Prior) on Sep 27, 2005 at 16:23 UTC

    Your code introduces a bug not in the original, here:

          overload::StrVal($_[0]) =~ /0x(\w+)/;

    [download]

    You use the same regexp as the original, but because you are no longer blessing into a known package the regexp may match the package name instead of the address. Indeed, a bug common enough to warrant the introduction of a new fatal error in perl-5.8 would give rise to exactly that situation:

      zen% cat t0
  package A; $x = bless {}; $y = bless [], $x; print "$y";

  zen% /opt/perl-5.6.1/bin/perl -wl t0
  A=HASH(0x811198c)=ARRAY(0x8111a94)

  zen% /opt/perl-5.8.0/bin/perl -wl t0
  Attempt to bless into a reference at t0 line 1.

    [download]

    Admittedly it is harder to get an overloaded object inadvertently in the wrong class like this, but "0x" is not so unusual a sequence of characters that it is fair to assume it will never appear in a legitimate package name. In any case it is easy enough to fix, with either /.*0x(\w+)/ or /0x(\w+)\)\z/.

    Hugo

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