My question is about nested map's/key's in a clojure atom and how to update them at the same time. In my case I have a nested map in another map which is a state holding atom of a little game.
This is my atom:
(def state (atom {:mousePos {:x 0 :y 0}
:playArea {:width 10000 :height 10000}
:player {:zoomOut 7.5
:cells [{:center {:x 1234 :y 5678}
:radius 17.84124116
:area 1000}]
:gravityCenter {:x 1234 :y 5678}
:gravityRadius 17.84124116}}))
And in this atom I want to update the mousePos x and y values at the same time to ensure their consistency/concurrency.
At the moment I'm doing:
(swap! state assoc-in [:mousePos :x] mouseX)
(swap! state assoc-in [:mousePos :y] mouseY)
But those are two swap!'s and theoretically if the thread where to switch in between I could end up with the problem, that for the following operations in the other thread, I would use the current x but the old y position of the mouse and I don't want that.
So I hoped to do something like this:
(swap! state assoc-in [:mousePos :x] mouseX
[:mousePos :y] mouseY)
Witch of course will not work so I tried writing my own assoc-in-mult function and that is where I'm unsuccessful.
When assoc-in doesn't fit with your use pattern because like you have here you want to update more than one value, then the more generic update-in or update functions tend to work well.
user> (def state (atom {:mousePos {:x 0 :y 0}}))
#'user/state
user> (swap! state update-in [:mousePos] assoc :x 123 :y 321)
{:mousePos {:x 123, :y 321}}
or when you have just one kay in the update path:
user> (swap! state update :mousePos assoc :x 123 :y 321)
{:mousePos {:x 123, :y 321}}