Better handling of namespaced keywords in maps with Clojure 1.9

Christoph Frick - ofnir.net

2016-10-10

Clojure 1.9 (or rather the alphas as of writing this) add some nice shortcuts to deal with maps containing namespaced keywords.

First of all there is now a reader macro #:ns{} to put the namespace on all keys in that map:

user=> (def customer #:customer{:id 42 :name "Acme"})
#'user/customer
user=> customer ; even prints as such
#:customer{:id 42, :name "Acme"}
user=> (assoc customer :something/else 23) ; once you mix, you get the regular output
{:customer/id 42, :customer/name "Acme", :something/else 23}
user=> (:customer/id customer) ; get works as expected
42
user=> #::{:id 23} ; also :: works as expected
#:user{:id 23}

The destructuring side of things got some enhancements too. The :keys destructuring not can also be used with a namespace:

user=> (let [{:customer/keys [id name]} customer] [id name])
[42 "Acme"]
user=> (def order #:order{:id 42
                          :customer customer
                          :items [#:order-item{:id 23
                                               :name "WiFi wire"
                                               :amount 2
                                               :price 64.0}]})
#'user/order
user=> (let [{{:customer/keys [id name]} :order/customer, :order/keys [items]} order]
         [id name (transduce (map (fn [{:order-item/keys [amount price]}] (* amount price))) + 0 items)])
[42 "Acme" 128.0]