Hello kennethk, You'll have to post a full code for that last output, because I have read your post more than five times and still don't understand the difference between weakening $self or weakening a copy of it.

Because $self immediately goes out of scope.
Well, $self and $closure_self are both lexicals of the same scope, so they both go out of scope at the same time, and the closure can close over any of the two and it shouldn't make any difference. By the way, here under perl v5.20, with my proposed code, I could never reproduce your last output:
main.pl 
use warnings;
no warnings 'redefine';
use strict;

use lib '.';
use Count;

print One::foo();
{
    my $bar = Count->mock;
    print One::foo();
}
print One::foo();

[download]
Count.pm 
package One;

sub foo {
    return "foo\n";
}
1;

package Count;

use Scalar::Util qw/weaken/; 

sub new {
    return bless {}, shift;
}
sub unmock {
    my $self = shift;
    *One::foo = \&{ $self->{sub} };
}
sub mock {
    my $thing = shift;
    my $self;

    if (ref($thing) eq __PACKAGE__){
        $self = $thing;
    }
    else {
        $self = bless {}, __PACKAGE__;
    }
    
    weaken $self;
    $self->{sub} = \&One::foo;
    *One::foo = sub { $self->{x} = 'x'; return "baz\n"; };
    return $self;
}
sub DESTROY {
    my $self = shift;
    print "destroying...\n";
    $self->unmock;
}
1;

[download]

In reply to Re^4: Trying to DESTROY() an object by Eily
in thread SOLVED: Trying to DESTROY() a (closure-wrapped) object by stevieb

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