Say I have a Java method that returns an object of some parent interface. The classes of the objects returned by this function are undocumented, however there is a rich and well documented hierarchy of interfaces all extending the parent interface. So for example:
public class Person {
public IMeal favoriteMeal() { ... }
}
public interface IBreakfast extends IMeal { ... }
public interface ILunch extends IMeal { ... }
public interface IBrunch extends IBreakfast, ILunch { ... }
If I knew (and was confident in the stability of) the underlying objects, I could write a multimethod to dispatch on the various objects returned by that method:
(defmulti place-setting class)
(defmethod place-setting Omelet [meal] ...)
However, since only the interfaces are public, I'd rather dispatch on those. Is there a (good) way to dispatch on interfaces? Perhaps like:
(defmulti place-setting magic-interface-dispatch-fn)
(defmethod place-setting IBreakfast [meal] ...)
This already works perfectly fine:
Note:
public interface IFn extends Callable, Runnable
public class Keyword implements IFn
And then:
(defmulti print-stuff class)
(defmethod print-stuff Callable [x] {:callable x})
(defmethod print-stuff :default [x] :not-found)
(print-stuff :foo) ;; => :callable
Note, multimethods always uses isa? internally on the (potentially custom) hierarchy. And (isa? Keyword Callable) is true.