Possible bug with reactions 'firing' unnecessarily in 0.6.0

[yatesco]

posted originally in reagent google group

My understanding is that a reaction is memoised and only executes the body the first time it is derefed since any atoms or reactions it deref's have changed.

Given this, and the following code:

(def active-stage-headers (ratom/reaction .....)
 
(defonce old-stage-header-ids (atom [])) ;; - a "normal" atom, not a reagent.ratom/atom
(def active-stage-header-ids
  (ratom/reaction
   (let [result (mapv (comp :id :patient) @active-stage-headers)]
     (if (= @old-stage-header-ids result)
       (js/console.log "recalculating stage-header-ids SAME!")
       (js/console.log "recalculating stage-header-ids DIFFERENT!"))
     (reset! old-stage-header-ids result)
     result)))

I would never expect to see more than one "recalculating stage-header-ids SAME!", however I am seeing that message appear in an endless loop (in Chrome).

I do see the expected behaviour in other reaction 'chains'.

Is this a bug or have I misunderstood - thanks.

[ducky427]

@yatesco, reagent atoms/reactions behave markedly differently when inside a reagent component.

Have you tried the same using a reagent component?

[yatesco]

Thanks @ducky427, that's interesting - I didn't realise this. Yes, both reactions are used independently inside components.

However, I still don't see that what I am doing (derefing a reaction inside another reaction) should cause that reaction to be fired over and over?

[yatesco]

Can anybody at least confirm whether this is a bug or have I misunderstood something?

[atroche]

I just tried this out on master, and when I deref'd it just printed this out once:
recalculating stage-header-ids DIFFERENT!

So maybe it's been inadvertently fixed?

[Deraen]

Can't reproduce.