On Wednesday, March 11, 2015 at 11:19:28 AM UTC+11, Mike Thompson wrote:
> This issue from David Nolen, caught my eye:
> https://github.com/andrewmcveigh/cljs-time/issues/21
>
> Feels like there is important information there, but I just don't know enough
> to interpret what's said. Can anyone help?
>
> If I have this:
>
> (def x {:a 1 :b 2})
>
> David is saying that x can't be dead-code-eliminated. Correct?
>
> If so, the solution he talks about is?
>
> ;; Replacing PersistentHashMaps with functions? Can't be right. I think I'm
> being too literal here
> (def x ((fn [] {:a 1 :b2})))
>
> ;; more likely this?
>
> (defn x
> []
> {:a 1 :b 2})
>
> Ie. you must now "call" x to get the map.
>
> If this solution is the right one, doesn't that mean we would be
> inefficiently constructing the (potentially large) hashmap inside x on each
> call.
Two follow-on questions:
- Could this problem with PersistentHashMaps not being dead code eliminated
be fixed with correct application of the Closure's "@nosideeffects" tags? Ie.
if the function which creates PersistentHashMaps had this tag in its comment?
- I assume that the following is not a problem:
(defn y [] :y)
(def x y)
If both x and y are never used then both will be dead code eliminated.
--
Mike
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