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#+OPTIONS: toc:nil num:nil #+TITLE: lazy-map [[https://travis-ci.org/Malabarba/lazy-map-clojure?branch%3Dmaster][https://secure.travis-ci.org/Malabarba/lazy-map-clojure.png?branch=master]] [[https://dry-clojure.herokuapp.com/repo/Malabarba/lazy-map-clojure/heads/master][https://img.shields.io/badge/dryness-68-97CA00.svg]] [[https://coveralls.io/github/Malabarba/lazy-map-clojure?branch=master][https://coveralls.io/repos/Malabarba/lazy-map-clojure/badge.svg?branch=master&service=github]]

Create maps whose values are only calculated when accessed, either from data or from java objects. Supports both Clojure and Clojurescript!

[[http://clojars.org/malabarba/lazy-map][file:https://clojars.org/malabarba/lazy-map/latest-version.svg]]

[[http://malabarba.github.io/lazy-map-clojure/][Documentation]]

** The [[http://malabarba.github.io/lazy-map-clojure/lazy-map.core.html#var-lazy-map][lazy-map]]

This macro is analogous to lazy-seq. It takes a map (instead of a seq), but the value expressions you write aren't actually evaluated until they are accessed.

#+BEGIN_SRC clojure user> (def my-map (lazy-map {:cause (do (println "Getting Cause") :major-failure) :name (do (println "Getting Name") "Some Name")})) #'user/my-map

user> (:name my-map) Getting Name "Some Name"

user> (:name my-map) "Some Name"

user> (:cause my-map) Getting Cause :major-failure

user> (:cause my-map) :major-failure #+END_SRC

You can also assoc new keys into a LazyMap like a regular Clojure map. If you assoc a delay it will act as a lazy value, and if you assoc anything else it acts as a regular value.

#+BEGIN_SRC clojure user> (def new-map (-> (assoc my-map :surname "Malabarba") (assoc :delayed-surname (delay (println "Resolved") "Late Malabarba")))) #'user/new-map user> (:surname my-map) "Malabarba" user> (:delayed-surname my-map) Resolved "Late Malabarba" #+END_SRC

** The [[http://malabarba.github.io/lazy-map-clojure/lazy-map.iop.html#var-extend-lazy-map][to-lazy-map]] protocol

This protocol allows you to convert any java class into a lazy map, where each entry correponds to a method call. Since everything is lazy, you can rest assured the methods won’t actually be called until you use them.

#+BEGIN_SRC clojure user> (use 'lazy-map.iop) nil user> (extend-lazy-map String) nil

user> (to-lazy-map "My Own Map!") {:to-char-array #object[clojure.lang.Delay 0x5c3c775a {:status :pending, :val nil}], :empty? #object[clojure.lang.Delay 0x774f63f2 {:status :pending, :val nil}], :to-string #object[clojure.lang.Delay 0x4a62ed8c {:status :pending, :val nil}], :intern #object[clojure.lang.Delay 0x4ddc7018 {:status :pending, :val nil}], :chars #object[clojure.lang.Delay 0x72e5585e {:status :pending, :val nil}], :class #object[clojure.lang.Delay 0x7e39e503 {:status :pending, :val nil}], :length #object[clojure.lang.Delay 0x236a69c5 {:status :pending, :val nil}], :trim #object[clojure.lang.Delay 0xd988100 {:status :pending, :val nil}], :bytes #object[clojure.lang.Delay 0x55671f45 {:status :pending, :val nil}], :code-points #object[clojure.lang.Delay 0x64c7f917 {:status :pending, :val nil}], :to-lower-case #object[clojure.lang.Delay 0x1493800b {:status :pending, :val nil}], :hash-code #object[clojure.lang.Delay 0x5d4a8318 {:status :pending, :val nil}], :object #object[clojure.lang.Delay 0x30ba32c3 {:status :pending, :val nil}], :to-upper-case #object[clojure.lang.Delay 0x6b6e6a82 {:status :pending, :val nil}]}

user> (:to-upper-case *1) "MY OWN MAP!" #+END_SRC

Note how there’s an entry for each method. Obviously, only methods that takes no arguments (0-arity) are included.

There’s also an extra :object entry holding the string itself.

** License

Copyright © 2015 Artur Malabarba

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.