yeah, I think records are the best approach, but I just struggle with them. Unfortunately I need an article or 2 on these to really get them. Last time I tried I was pretty unsuccessful.
On Nov 13, 11:41 am, Chris Maier <christopher.ma...@gmail.com> wrote: > Another approach would be to use records and protocols: > > (defprotocol HasCees > (c [this] "Returns a 'c'")) > > (defrecord Foo [a b] > HasCees > (c [this] > (+ (:a this) (:b this)))) > > Now, to use it: > > user> (def my-foo (Foo. 1 2) > #'user/my-foo > user> (c my-foo) > 3 > > This is practically a drop-in replacement for the struct-based code > (since Clojure records behave like maps). I think with the advent of > records, there isn't really any reason to use structs anymore. Also, > this is arguably more fitting with the semantics you have, as the "c" > is more of a behavior than a value. > > It's also common to have a factory function to create record instances > (just as Michel showed with structs), like this: > > (defn make-a-foo [a b] > (Foo. a b)) > > This helps to make dealing with the positional constructors of records > a bit less awkward. > > Here's some links:http://clojure.org/datatypeshttp://clojure.org/protocols > > Hope that helps, > Chris > > On Sat, Nov 13, 2010 at 11:48 AM, Michel Alexandre Salim > > > > > > > > <michel+...@michelsylvain.info> wrote: > > On Sat, 13 Nov 2010 06:31:03 -0800, garf wrote: > > >> If I have a struct whose creation will require some function calls that > >> references some of its members, I am unsure how to go about it in a > >> clean way. For example: > >> (defstruct tz :a :b :c) > > >> (def tz1 1 2 (+ (:a tz1) (:b tz1)) > > > Could you give a more realistic example of how you plan to use this? > > > If the only restriction is that you only know the values for :a and :b at > > the time you want to create the structure, then this would work: > > > (defn create-tz [a-val b-val] > > (struct-map tz :a a-val :b b-val :c (some-fn a-val b-val))) > > >> will not work, but reflects the problem. Ideally at the end of this I > >> could do (:c tz1) and get 3 back. Any suggestions? Originally I had > >> used assocs, but that runs into the immutability problem, for example > > >> (defstruct tz :a :b) > >> (def tz1 1 2) > >> (assoc tz1 :c (+ (:a tz1) (:b tz1)) > > >> does not actually update tz1 > > > Correct. Values are immutable, and in Clojure, even collections are > > values! > > > If you want to have a variable hold a reference to some changing values > > then what you want is to use an atom or a ref. Atom is more easy to use, > > and unless you have several mutable values that need concurrent updating, > > is sufficient, so here's an example: > > >> (def tz1 (atom (struct-map tz :a 1 :b 2))) > > #'user/tz1 > >> @tz1 > > {:a 1, :b 2, :c nil} > >> (swap! tz1 #(assoc % :c (+ (:a %) (:b %)))) > > {:a 1, :b 2, :c 3} > >> @tz1 > > {:a 1, :b 2, :c 3} > > > Hope that helps, > > > -- > > Michel Alexandre Salim > > Clojure contributor:http://clojure.org/contributing > > GPG key ID: 78884778 > > > µblog:http://identi.ca/hircus | Jabber: hir...@jabber.ccc.de > > http://twitter.com/hircus| IRC: hir...@irc.freenode.net > > > () ascii ribbon campaign - against html e-mail > > /\ www.asciiribbon.org - against proprietary attachments > > > -- > > 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
