Keeping track of the number of instances can very well be done via DESTROY. I wouldn't put in a reference in the object though. Then you make the count accessable outside your class, and you probably don't want to do that.

Use something like:

    package MyClass;
        
    my $count = 0;
        
    sub new {
        my $proto = shift;   
        my $class = ref $proto || $proto;
        $count ++;
        my $obj = ....;
        bless $obj => $class;
    }

    sub DESTROY {
        $count --;
    }
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And do not call DESTROY yourself. Perl will do that for you.

Abigail