In general, it's tough, partly because Perl's such a dynamic language and partly because it's a question of design. If I were in your shoes, I'd likely save the class name as it came into the constructor.

If you really need to compare references, one approach is take a reference to the method within the class. It's easiest to do that with symbolic references. That should be one warning against the idea...

package Foo;

sub foo {}

package Bar;

@Bar::ISA = 'Foo';

sub bar {}

package main;

my $bar = bless {}, 'Bar';

my $foo      = $bar->can( 'foo' );
my $fooinbar = do
{
    no strict 'refs';
    my $subname = ref $foo . '::foo';
    \&{ ref $foo . '::foo' } if defined *{ $subname }{CODE};
};

print "$foo -> $fooinbar\n";
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