What's the clojure way to builder pattern?

Question

We usually use builder pattern in java, like this:

UserBuilder userBuilder = new UserBuilder();
User John = userBuiler.setName("John")
                      .setPassword("1234")
                      .isVip(true)
                      .visableByPublic(false)
                      .build();

Some of the attributes have default value, and some haven't.

Passing attributes in a map may be a solution, but it makes the argument really longer:

(def john (make-user {:name "John" :pass "1234" :vip true :visible false}))

So, my question is, is there a elegant way to achieve this?

Answer 1

If you want to construct some clojure structure, you can use destructuring pattern in function arguments. You will then achieve the similar thing you have already wrote.

(defn make-user [& {:keys [name pass vip visible]}]
  ; Here name, pass, vip and visible are regular variables
  ; Do what you want with them
)

(def user (make-user :name "Name" :pass "Pass" :vip false :visible true))

I doubt that you can do something in less code than this.

If you want to construct Java object (using its setters), you can use the approach Nicolas suggested.

Answer 2

I would normally pass attributes in via a map - there's no real issue with doing this since the attribute map is really just one argument to the make-user function. You can also do nice stuff inside make-user like merge in default attributes.

If you really want to construct such a map with a builder pattern, you can do it with a threading macro as follows:

(def john 
  (-> {}
    (assoc :name "John")
    (assoc :pass "1234")
    (assoc :vip true)
    (assoc :visible false)
    make-user))