use Contextual::Return;

sub blahblah {
  ## ...
  return (
    STR { _special_to_string( $retval ); }
    HASHREF { +{ special => $retval, string => _special_to_string( $retval ) }; }
  );
}

my $foo = blahblah( @some_args );
say "Foo: $foo";
say "Special from foo: ", $foo->{special};