(nothing to add, just wanted to say that explanation has certainly clarified things for me. These excellent replies, as oppose to "go read XYZ" really differentiate this community! Thanks again)
On 28 July 2011 12:46, Alex Osborne <a...@meshy.org> wrote: > Oskar <oskar.kv...@gmail.com> writes: > > > I have not heard much about records and protocols. What is a typical > > use case in idiomatic Clojure code for them? Is it a good idea, for > > example, to make a "Character" protocol and "Player" and "Monster" > > records or something in a game. It feels a bit too much like OOP for > > me to be comfortable with it, but I can't immediately see why that > > would be bad. I just don't know how they are supposed to be used. > > The primary purpose of protocols is efficient, extensible polymorphism: > handling different data types using a uniform interface. > > Rather than a composite idea like "Character" it is preferable to use > many fine-grained protocols that each cover a single indivisible > concept. Depending on the mechanics in your game you might have > protocols like Damagable, Listener, Throwable, Describable, Capturable, > Clickable, Edible, Castable and Container. > > (defprotocol Damagable > (alive? [damagable]) > (damage [damagable weapon])) > > (defprotocol Describable > (describe [describable])) > > (defrecord Monster [strength color] > Damagable > (alive? [m] (pos? health) > (damage [m weapon] (update-in m [:health] - (weapon :power)))) > Describable > (describe [m] (str (if (> health 90) "a healthy " "an injured ") > (if (> strength 50) "powerful " "weak ") > color " monster"))) > > (defrecord Tree [age species] > Describable > (describe [t] (str (when (> age 100) "an ancient " "a ") > species " tree"))) > > One of the lovely things about protocols is that they are very > extensible. Suppose you want to write some graphics code for drawing > different game entities. You can define a rendering protocol and extend > it to your entities all in a different file. You don't have to clutter > up your game logic files with the ugly drawing code. > > ;; gfx.clj > > (ns game.gfx > (:require [game.enemies :as enemies] > [game.scenary :as scenary])) > > (defprotocol Renderable > (paint [x canvas]) > (pixel-width [x])) > > (extend-protocol Renderable > scenary/Rock > (paint [tree canvas] (blit canvas "rock.png")) > (pixel-width [tree] 30) > scenary/Tree > (paint [tree canvas] (blit canvas "tree.png")) > (pixel-width [tree] 150) > enemies/Monster > (paint [m canvas] (blit canvas (get icons (:activity m)))) > (pixel-width [m] 70)) > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
