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Linked

Map and Set structures that rememeber the insertion order of its elements, even after multiple assoc and dissoc. For Clojure and ClojureScript.

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Map

(require '[linked.core :as linked])

(linked/map :b 2 :a 1 :d 4)
;=> #linked/map [[:b 2] [:a 1] [:d 4]]

(assoc (linked/map :b 2 :a 1 :d 4) :c 3)
;=> #linked/map [[:b 2] [:a 1] [:d 4] [:c 3]]

(into (linked/map) [[:c 3] [:a 1] [:d 4]])
;=> #linked/map [[:c 3] [:a 1] [:d 4]]

(dissoc (linked/map :c 3 :a 1 :d 4) :a)
;=> #linked/map [[:c 3] [:d 4]]

Set

(require '[linked.core :as linked])

(linked/set 4 3 1 8 2)
;=> #linked/set [4 3 1 8 2]

(conj (linked/set 9 10) 1 2 3)
;=> #linked/set [9 10 1 2 3]

(into (linked/set) [7 6 1 5 6])
;=> #linked/set [7 6 1 5]

(disj (linked/set 8 1 7 2 6) 7)
;=> #linked/set [8 1 2 6]

Performance

These data structures wrap a normal hash-map but instead of feeding it a normal [key value] pair their remeber a [key value left-key right-key] record. When an item is removed from the data structure it is sufficient to update the left and right node to reference each others keys while removing the chosen node. This implementation yields the same Big O time and space complexity of a standard hash-map (altought effective performance will be slower by a constant factor).

Comparison with ordered

Ordered will keep on allocating memory space until you explicitly call compact to clean up the garbage. Linked doesn't keep a pointer to old elements
Ordered has transient support for faster allocation of a large number of items
Linked works with ClojureScript

License

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.