How about something like this? You can still keep your cache as an atom
that you can pass around, and you avoid unnecessary recomputation through
memoize:
(def cache (atom {}))
(def lookup
(let [calc-value* (memoize calc-value)]
(fn [cache k]
(when-not (contains? @cache k)
(swap! cache assoc k (calc-value* k)))
(@cache k))))
Den lördagen den 30:e augusti 2014 kl. 12:11:58 UTC+2 skrev Colin Fleming:
>
> In my case I can't use memoize because I need to supply the cache map -
> that in turn is stored on another object so it can be invalidated by events
> outside my control.
>
>
> On 30 August 2014 20:00, Ray Miller <[email protected] <javascript:>>
> wrote:
>
>> On 30 August 2014 06:26, Colin Fleming <[email protected]
>> <javascript:>> wrote:
>> >
>> > I want to use a map to cache values based on a key. I'm planning to use
>> an
>> > atom for this. My basic operation is "give me the value for this key" -
>> if
>> > the value exists in the map then that value should be returned,
>> otherwise a
>> > new value should be calculated, inserted in the map and then returned.
>> My
>> > plan is to implement something like the following:
>> >
>> >
>> > (defn ensure [cache key]
>> > (if (contains? cache key)
>> > cache
>> > (assoc cache key (calc-value key))))
>> >
>> > (let [value (get (swap! cache ensure key) key)]
>> > ... do my thing with value ...)
>>
>> Why not just use memoize?
>>
>> (def calc-value (memoize (fn [key] ...))
>>
>> If you need more control over the cache, check out core.memoize (which
>> builds on top of core.cache).
>>
>> Ray.
>>
>> --
>> You received this message because you are subscribed to the Google
>> Groups "Clojure" group.
>> To post to this group, send email to [email protected]
>> <javascript:>
>> Note that posts from new members are moderated - please be patient with
>> your first post.
>> To unsubscribe from this group, send email to
>> [email protected] <javascript:>
>> For more options, visit this group at
>> http://groups.google.com/group/clojure?hl=en
>> ---
>> You received this message because you are subscribed to the Google Groups
>> "Clojure" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to [email protected] <javascript:>.
>> For more options, visit https://groups.google.com/d/optout.
>>
>
>
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to [email protected]
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
[email protected]
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
---
You received this message because you are subscribed to the Google Groups
"Clojure" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
For more options, visit https://groups.google.com/d/optout.
