fx-vs-fm.clj

;; One example of why one might want to generate platform specific feature macros

;; I'm not saying this is a good DSL, just possible with https://github.com/feature-macros/clojurescript/tree/feature-macros/feature-macros-demo
(deftype-unified Foo [bar]
  unified/Counted [(count [_] {:cljs (-count bar)
                               :clj (.count bar)})]
  BazProtocol
  (fizz [_] :buzz))

;; where unified/Counted [...] expands to clojure.lang.Counted/count on :clj and ICounted/-count on :cljs

;; vs reified instances of #+clj #+cljs *every* *single* *time* we need to paper over implementation differences

(deftype Foo [bar]
#+clj clojure.lang.Counted
#+cljs ICounted
#+clj (count [_] (.count bar))
#+cljs (-count [_] (-count bar))
  BazProtocol
  (fizz [_] :buzz))

;; IIR, one of Clojure's guiding design principles is to not add features that make future need X impossible
;; Without first-class data representation, feature expressions run counter to that principle