sub what_does_it_return () return classA | classH {
   return rand(1) > 0.5 
        ? bless( [], 'classA' )
        : bless( {}, 'classH' );
}

##</code><code>##

my classA | classH $x = what_does_it_return();

##</code><code>##

$x->something()

##</code><code>##

package classA;
sub something (classA $self) { ... }

##</code><code>##

sub what_does_it_return () return classX {
   return rand(1) > 0.5 
        ? bless( [], 'classA' )
        : bless( {}, 'classH' );
}

##</code><code>##

my classX $x = what_does_it_return();
$x->something() # compile-time blowup, classX doesn't have the "something" method!