Allrighty that works, thanks a lot.
haven't debugged a whole lot of clojure, but update-in makes sense.
thanks!
On Friday, October 24, 2014 5:18:01 PM UTC+2, Fluid Dynamics wrote:
>
> On Friday, October 24, 2014 11:14:56 AM UTC-4, Fluid Dynamics wrote:
>>
>> On Friday, October 24, 2014 10:42:37 AM UTC-4, Kasper Jordaens wrote:
>>>
>>> Hey,
>>>
>>> I've been experimenting with newtonian, I love it, but I have a simple
>>> question, because I'm stuck
>>>
>>> after adding some emitters
>>>
>>> [#newtonian.corporum.ParticleEmitter{:position
>>> #newtonian.utils.Vector2D{:x 23.0, :y 280.0}, :velocity
>>> #newtonian.utils.Vector2D{:x 0.0, :y 10.0}, :size 8, :life -1, :spread
>>> 0.09817477042468103, :emission-rate 4}
>>> #newtonian.corporum.ParticleEmitter{:position #newtonian.utils.Vector2D{:x
>>> 200.0, :y 280.0}, :velocity #newtonian.utils.Vector2D{:x 0.0, :y 10.0},
>>> :size 8, :life -1, :spread 0.09817477042468103, :emission-rate 4}]
>>>
>>>
>>> I want to dynamically change them but this seems to be inaccessible as
>>> an atom?
>>>
>>> I can get to individual objects like
>>>
>>> (get (nth @newt/emitters 0) :position) ==> #newtonian.utils.Vector2D{:x
>>> 23.0, :y 280.0}
>>>
>>>
>>> but how can I swap the atom at Vector2D?
>>>
>>>
>>> (swap! (get (nth @newt/emitters 0) :position) :x 200) ==> java.lang.
>>> ClassCastException: newtonian.utils.Vector2D cannot be cast to clojure.
>>> lang.Atom core.clj:2233 clojure.core/swap!
>>>
>>>
>> What you want here is update-in. Try
>>
>> (swap! newt update-in [:emitters 0 :position] assoc :x 200)
>>
>> assuming that @newt is a map with an :emitters key. I'm not familiar with
>> the library and I'm not even sure what kind of object could be in the atom
>> newt that @newt/emitters makes sense, but when you want to "change" a thing
>> buried deep in a nested associative data structure the usual tool for that
>> is update-in.
>>
>
> I looked briefly at the newtonian docs and it looks like newt/emitters is
> the atom, hmm, global vars? Anyway you just want
>
> (swap! newt/emitters update-in [0 :position] assoc :x 200)
>
> then, to replace the value of x in the first emitter. You could also use
>
> (swap! newt/emitters update-in [0 :position :x] + 100)
>
> and the like to "move" that emitter's x around relative to where it was,
> here 100 units further right one presumes.
>
>
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