extend-type

added
1.2

ns
clojure.core

type
macro

(extend-type t & specs)

A macro that expands into an extend call. Useful when you are
supplying the definitions explicitly inline, extend-type
automatically creates the maps required by extend.  Propagates the
class as a type hint on the first argument of all fns.

(extend-type MyType 
Countable
(cnt [c] ...)
Foo
(bar [x y] ...)
(baz ([x] ...) ([x y & zs] ...)))

expands into:

(extend MyType
Countable
{:cnt (fn [c] ...)}
Foo
{:baz (fn ([x] ...) ([x y & zs] ...))
:bar (fn [x y] ...)})

                ;;; This is a library for the shopping result.

(defrecord Banana [qty])

;;; 'subtotal' differ from each fruit.

(defprotocol Fruit
  (subtotal [item]))

(extend-type Banana
  Fruit
  (subtotal [item]
    (* 158 (:qty item))))

;;; Please see the term of 'reify'.