Overriding CORE::GLOBAL::bless

rinceWind has asked for the wisdom of the Perl Monks concerning the following question:

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;
    }
}
[download]

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.

--

Oh Lord, won’t you burn me a Knoppix CD ?
My friends all rate Windows, I must disagree.
Your powers of persuasion will set them all free,
So oh Lord, won’t you burn me a Knoppix CD ?
(Missquoting Janis Joplin)

Comment on Overriding CORE::GLOBAL::bless Download Code

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Re: Overriding CORE::GLOBAL::bless by chromatic (Archbishop) on Aug 19, 2005 at 17:08 UTC
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' );` [download]	[reply] [d/l]
Re: Overriding CORE::GLOBAL::bless by sh1tn (Priest) on Aug 19, 2005 at 12:23 UTC
You may want to use subs pragma for overriding: `use subs qw(bless);` [download] Update: In fact you have to use module or subs pragma in order ro override in CORE::GLOBAL.	[reply] [d/l]
Re^2: Overriding CORE::GLOBAL::bless by rinceWind (Monsignor) on Aug 19, 2005 at 13:03 UTC
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. -- Oh Lord, won’t you burn me a Knoppix CD ? My friends all rate Windows, I must disagree. Your powers of persuasion will set them all free, So oh Lord, won’t you burn me a Knoppix CD ? (Missquoting Janis Joplin)	[reply] [d/l]
Re: Overriding CORE::GLOBAL::bless by dragonchild (Archbishop) on Aug 19, 2005 at 17:34 UTC
Are you positive bless is overiddable or is it like print? My criteria for good software: Does it work? Can someone else come in, make a change, and be reasonably certain no bugs were introduced?	[reply]
Re^2: Overriding CORE::GLOBAL::bless by rinceWind (Monsignor) on Aug 20, 2005 at 00:13 UTC
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. -- Oh Lord, won’t you burn me a Knoppix CD ? My friends all rate Windows, I must disagree. Your powers of persuasion will set them all free, So oh Lord, won’t you burn me a Knoppix CD ? (Missquoting Janis Joplin)	[reply]
Re: Overriding CORE::GLOBAL::bless by fro (Novice) on Jan 31, 2006 at 12:13 UTC
> 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.	[reply]
Re^2: Overriding CORE::GLOBAL::bless by rinceWind (Monsignor) on Jan 31, 2006 at 15:20 UTC
Yup, that's what I found. I didn't post my conclusion here, but to my use.perl journal. -- Oh Lord, won’t you burn me a Knoppix CD ? My friends all rate Windows, I must disagree. Your powers of persuasion will set them all free, So oh Lord, won’t you burn me a Knoppix CD ? (Missquoting Janis Joplin)	[reply]