Another page exploring the Clojure API.
Today, it’s conj.
Added 2017-10-04_22.55.23
(def my-map (hash-map :a 1 :b 2 :c 3))
my-map
=> {:c 3, :b 2, :a 1}
(conj my-map :d 4)
=> java.lang.IllegalArgumentException: Don't know how to create ISeq from: clojure.lang.Keyword
;; with assoc, you can list key/val pairs as separate args
;; with conj, they have to be in a map format
(conj my-map {:d 4})
=> {:c 3, :b 2, :d 4, :a 1}
;; our original map stays the same
my-map
=> {:c 3, :b 2, :a 1}
;; we can work with vectors too
(def my-vec [1 2 3 4])
;; element goes at the end
(conj my-vec 5)
=> [1 2 3 4 5]
;;conj-ing won't change our original vector
my-vec
=> [1 2 3 4]
(def my-list '(1 2 3 4))
;; conj puts new element at beginning of list
(conj my-list 5)
=> (5 1 2 3 4)
my-list
=> (1 2 3 4)
(def my-set (set '(1 2 3 4 4)))
my-set
=> #{1 4 3 2}
(conj my-set 5)
=> #{1 4 3 2 5}
;; trying to add an element in the set is ignored
(conj my-set 3)
=> #{1 4 3 2}
;; original not changed
my-set
=> #{1 4 3 2}
;; it seems to put elements in a set in random places
(conj my-set 66)
=> #{1 4 3 2 66}
(conj my-set 22)
=> #{1 4 22 3 2}
;; you can conj nil, true and false
(conj my-vec nil)
=> [1 2 3 4 nil]
(conj my-set nil)
=> #{nil 1 4 3 2}
(conj my-set false)
=> #{1 4 3 2 false}
(conj my-set true)
=> #{1 4 true 3 2}
(conj my-list true)
=> (true 1 2 3 4)
You’re welcome.