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Using
note: see the page on including core.memoize before you begin this section
To use the memoization cache implementations you first need to require the proper namespace:
(require '[clojure.core.memoize :as memo])Next you can create some function that you'd like to memoize. For illustrative purposes I'll create one that is intentionally slow:
(defn slowly [n]
(Thread/sleep 5000)
n)I can then memoize this function using core.memoize/memo which is an augmented replacement for clojure.core/memoize:
(def once-slowly (memo/memo slowly))
(once-slowly 42)
;; wait 5 seconds
;;=> 42
(once-slowly 42)
;; instantly
;;=> 42One advantage of using the clojure.core.memoize/memo function over the one provided in Clojure is that the former allows you to evict certain enties as needed, shown next.
To explicitly evict an element in a memoization cache, use the clojure.core.memoize/memo-clear! function:
(memo/memo-clear! once-slowly [42])
(once-slowly 42)
;; wait 5 seconds
;;=> 42The argument to clojure.core.memoize/memo-clear! is a vector of the precise argument values that you'd like to clear. You can not pass the argument vector to instead clear the entire memoization cache for a function.
You could also use a memoization strategy that will expire its entries based on an expiration parameter, shown below:
(def sometimes-slowly (memo/ttl slowly :ttl/threshold 10000))
(sometimes-slowly 42)
;; wait 5 seconds
;;=> 42
(sometimes-slowly 42)
;; instantly
;;=> 42The :ttl/threshold flag states that entries in the memoization cache older than 10,000 milliseconds (10 seconds) should be evicted from the internal cache. If you wait some time after running the code above, you should see the function call slow down again:
(sometimes-slowly 42)
;; wait 5 seconds
;;=> 42For specific information about eviction policies and thresholds, view the specific documentation for each cache type listed in the next section.
core.memoize comes with a number of builtin memoization cache implementations, including (click through for specific information):
Enjoy.