Data commit

Task/Delegates/NGS/delegates.ngs

@@ -0,0 +1,40 @@
+{
+	type Delegator
+
+	F init(d:Delegator) d.delegate = null
+
+	F default_impl(d:Delegator) 'default implementation'
+
+	F operation(d:Delegator) default_impl(d)
+
+	F operation(d:Delegator) {
+		guard defined thing
+		guard thing is Fun
+		try {
+			d.delegate.thing()
+		}
+		catch(e:ImplNotFound) {
+			# Might be unrelated exception, so check and optionally rethrow
+			e.callable !== thing throws e
+			default_impl(d)
+		}
+	}
+
+	F operation(d:Delegator) {
+		guard d.delegate is Null
+		default_impl(d)
+	}
+
+
+	a = Delegator()
+	echo(a.operation())
+
+	# There is no method thing(s:Str)
+	a.delegate = "abc"
+	echo(a.operation())
+
+	# ... now there is method thing(s:Str)
+	F thing(s:Str) 'delegate implementation'
+	echo(a.operation())
+	
+}