Clojure has two types of maps. The PersistentArrayMap and the PersistentHashMap data types are responsible for key-value collections. The only exception is the PersistentHashSet data type, which looks like #{:key-here :key-here}. The difference between a Map and a Set is that the key is the value in a set, where as a key holds a separate value in a Map.
The
hash-map form can be used to make a key-value collection:
user> (def -hmap (hash-map :key1 "value" :key2 "value2"))
#'user/-hmap
user> (vals -hmap)
("value2" "value")
user> (keys -hmap)
(:key2 :key1)
user> (:key2 -hmap)
"value2"The
array-map form can do the same:
user> (def -amap (array-map "a" 1 "b" 2))
#'user/-amap
user> (keys -amap)
("a" "b")Remember to use the get form when needing to set default values for missing keys:
user> (get -amap "a" :not-found) 1 user> (get -amap "c" :not-found) :not-found user> (-hmap :key2) "value2" user> (-hmap :key3) nil user> (-hmap :key3 :not-found...