Presuming he uses the W::M::Link instances then his $mech->get( $foo ) calls should Do The Right Thing™ for relative URLs, but yup very good point about absolutifying before comparing (and the URI::URL instances url_abs returns stringifies sanely when you use it as a hash key, so if you're not going to subsequently pass them on to a get call you could use a variation of your (the OP's)original code: my %seen; @seen{ map $_->uri_abs, @links ) = ();my @out = keys %seen;).