Clojure get nested map value

Question

So I'm used to having a nested array or map of settings in my applications. I tried setting one up in Clojure like this:

(def gridSettings
  {:width 50
   :height 50
   :ground {:variations 25}
   :water {:variations 25}
   })

And I wondered if you know of a good way of retrieving a nested value? I tried writing

(:variations (:ground gridSettings))

Which works, but it's backwords and rather cumbersome, especially if I add a few levels.

Answer 1

That's what get-in does:

(get-in gridSettings [:ground :variations])

From the docstring:

clojure.core/get-in
([m ks] [m ks not-found])
  Returns the value in a nested associative structure,
  where ks is a sequence of keys. Returns nil if the key
  is not present, or the not-found value if supplied.

Answer 2

You can use the thread-first macro:

(-> gridSettings :ground :variations)

I prefer -> over get-in except for two special cases:

• When the keys are an arbitrary sequence determined at runtime.
• When supplying a not-found value is useful.