Overriding CORE::GLOBAL::bless

[rinceWind]

I've decided to work on my Devel::Leak::Object, as I need to do some leak tracing in a Class::DBI app.

To date, I've only been able to use it in cases like this manually tracking objects, as setting CORE::GLOBAL::bless during BEGIN interferes with initialisation of several things including the debugger. I had an idea that we could set CORE::GLOBAL::bless in a callable sub, thus:

sub track_blessings {
    my $type = shift;

    if ($type =~ /^global$/i) {
            *CORE::GLOBAL::bless = \&bless;
    }
}

The trouble is, that this does not seem to work. The original technique of setting it inside an import routine works fine (see the source code for Devel-Leak-Object-0.02 on CPAN, in particular test t/004_auto.t). I've been staring at my track_blessings routine, and I can't see a reason why this override is not happening. Maybe I need another cup of coffee.

[sh1tn]

You may want to use subs pragma for overriding:

use subs qw(bless);

Update: In fact you have to use module or subs pragma in order ro override in CORE::GLOBAL.

[rinceWind]

Added use subs qw(bless); this has made no difference whatsoever. The track_blessings sub is performing the typeglob assignment to CORE::GLOBAL::bless, but Devel::Leak::Object::bless is not getting called.

[chromatic]

This is tricky. I've found that using the subs pragma in the package space of the package in which you want to override an operator before you load the module normally seems to work:

use Test::More tests => 2;

package CGI;
use subs 'bless';

package main;

my $called = 0;

use CGI;
sub CGI::bless
{
    $called++;
    CORE::bless( $_[0], $_[1] );
};

my $foo = CGI->new();
is( $called, 1, 'bless() should call overridden version' );
isa_ok( $foo, 'CGI', 'which should return something that' );

[dragonchild]

Are you positive bless is overiddable or is it like print?

[rinceWind]

The point is that I am successfully doing this from an importer sub, as per Devel::Leak::Object 0.02 - and it gets called. But I want to achieve the same thing later on under user control, after BEGIN has finished.

[fro]

> I've been staring at my track_blessings routine, and I can't see a reason why this override is not happening.
That's because you cannot override built-in functions
during runtime - when perl is _compiling_ this line:

bless $foo, "Bar";

it decides what op code to generate (in that case what function to
invoke). This happens at compile time. After that, when
you call your track_blessings() it is too late - the
calling of CORE::bless is already compilied and hardcoded
in the syntax opcode tree.

[rinceWind]

Yup, that's what I found. I didn't post my conclusion here, but to my use.perl journal.