raku-rosettacode/programming_tasks/D/Delegates.md

Delegates

class Non-Delegate  { }
 
class Delegate {
	method thing {
		return "delegate implementation"
	}
}
 
class Delegator {
	has $.delegate is rw;
 
	method operation {
		$.delegate.^can( 'thing' ) ?? $.delegate.thing
		!! "default implementation"
	}
}
 
my Delegator $d .= new;
 
say "empty: "~$d.operation;
 
$d.delegate = Non-Delegate.new;
 
say "Non-Delegate: "~$d.operation;
 
$d.delegate = Delegate.new;
 
say "Delegate: "~$d.operation;