Why Not a Function #5: update-if

(defn update-if [m k f] (if (contains? m k) (update m k f) m))

update-if is similar to update. The only difference is that it does nothing if the associative structure does not contain the key so there is nothing to update.

(update {:speed 0} :speed str)
=> {:speed "0"}

(update {:velocity 0} :speed str)
=> {:velocity 0, :speed ""}

(update-if {:speed 0} :speed str)
=> {:speed "0"}

(update-if {:velocity 0} :speed str)
=> {:velocity 0}

Written on March 16, 2020