September 2017 Update

Task/Constrained-genericity/OoRexx/constrained-genericity.rexx

@@ -0,0 +1,29 @@
+call dinnerTime "yogurt"
+call dinnerTime .pizza~new
+call dinnerTime .broccoli~new
+
+
+-- a mixin class that defines the interface for being "food", and
+-- thus expected to implement an "eat" method
+::class food mixinclass object
+::method eat abstract
+
+::class pizza subclass food
+::method eat
+  Say "mmmmmmmm, pizza".
+
+-- mixin classes can also be used for multiple inheritance
+::class broccoli inherit food
+::method eat
+  Say "ugh, do I have to?".
+
+::routine dinnerTime
+  use arg dish
+  -- ooRexx arguments are typeless, so tests for constrained
+  -- types must be peformed at run time.  The isA method will
+  -- check if an object is of the required type
+  if \dish~isA(.food) then do
+     say "I can't eat that!"
+     return
+  end
+  else dish~eat