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function-cachefunctools

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Yesterday I've reviewed fare-memoization and decided to tell you about function-cache, the library I'm using for memoization instead.

The main features are its ability to set TTL and an extendable caching protocol which allows to use different kinds of caches.

For example, here we'll use LRU cache which will remember only 3 results:

POFTHEDAY> (function-cache:defcached (foo :cache-class 'function-cache:lru-cache
                                          :capacity 3)
               (param)
             (format t "Not cached, returning the value: ~A~%" param)
             param)

POFTHEDAY> (foo 1)
Not cached, returning the value: 1
1

;; Now the value returned from the cache:
POFTHEDAY> (foo 1)
1

;; Let's fill the cache:
POFTHEDAY> (foo 2)
Not cached, returning the value: 2
2
POFTHEDAY> (foo 3)
Not cached, returning the value: 3
3
POFTHEDAY> (foo 4)
Not cached, returning the value: 4
4
POFTHEDAY> (foo 5)
Not cached, returning the value: 5
5

;; Value for 1 was evicted from the cache:
POFTHEDAY> (foo 1)
Not cached, returning the value: 1
1

And here is how we can set TTL and make the function result remembered for 5 seconds:

POFTHEDAY> (function-cache:defcached (foo :timeout 5)
               ()
             (let ((ts (local-time:now)))
               (format t "Not cached, returning the value: ~A~%" ts)
               ts))

POFTHEDAY> (foo)
Not cached, returning the value: 2020-09-09T22:36:05.630085+03:00
@2020-09-09T22:36:05.630085+03:00

POFTHEDAY> (foo)
@2020-09-09T22:36:05.630085+03:00

POFTHEDAY> (foo)
@2020-09-09T22:36:05.630085+03:00

POFTHEDAY> (foo)
@2020-09-09T22:36:05.630085+03:00

POFTHEDAY> (foo)
Not cached, returning the value: 2020-09-09T22:36:10.767777+03:00
@2020-09-09T22:36:10.767777+03:00

Sometimes it can be very convenient to cache rarely changed data this way.