langs a-z

Task/Delegates/Oz/delegates.oz

@@ -0,0 +1,43 @@
+declare
+  class Delegator from BaseObject
+     attr
+	delegate:unit
+
+     meth set(DG)
+	{Object.is DG} = true %% assert: DG must be an object
+	delegate := DG
+     end
+
+     meth operation($)
+	if @delegate == unit then
+	   {self default($)}
+	else
+	   try
+	      {@delegate thing($)}
+	   catch error(object(lookup ...) ...) then
+	      %% the delegate did not understand the message
+	      {self default($)}
+	   end
+	end
+     end
+
+     meth default($)
+	"default implementation"
+     end
+  end
+
+  class Delegate from BaseObject
+     meth thing($)
+	"delegate Implementation"
+     end
+  end
+
+  A = {New Delegator noop}
+in
+  {System.showInfo {A operation($)}}
+
+  {A set({New BaseObject noop})}
+  {System.showInfo {A operation($)}}
+
+  {A set({New Delegate noop})}
+  {System.showInfo {A operation($)}}