Data commit

Task/Delegates/Pop11/delegates.pop11

@@ -0,0 +1,32 @@
+uses objectclass;
+define :class Delegator;
+    slot delegate = false;
+enddefine;
+
+define :class Delegate;
+enddefine;
+
+define :method thing(x : Delegate);
+   'delegate implementation'
+enddefine;
+
+define :method operation(x : Delegator);
+if delegate(x) and fail_safe(delegate(x), thing) then
+   ;;; Return value is on the stack
+else
+   'default implementation'
+endif;
+enddefine;
+
+;;; Default, without a delegate
+lvars a = newDelegator();
+operation(a) =>
+
+;;; a delegating to itself (works because Delegator does not
+;;; implement thing)
+a -> delegate(a);
+operation(a) =>
+
+;;; delegating to a freshly created Delegate
+newDelegate() -> delegate(a);
+operation(a) =>