Hi Meikel,
This is awesome! You just did a big chunk of what I was about to try
to do :). Sorry for the late response, I've been off the grid for a
few days...
With your second proposed solution, the defrecord-with-defaults macro,
one can achieve very good performance while keeping some of the
features that implementation inheritance provides. I'll look into your
macro more closely and see if I can make it a seamless substitute for
defmacro.
Toni.
On Sat, Jul 17, 2010 at 4:02 AM, Meikel Brandmeyer <m...@kotka.de> wrote:
> Hi,
>
> one way to do that is using extend.
>
> (def defaults
> {fn1 (fn ...)
> fn2 (fn ...)
> fn3 (fn ...)})
>
> (defrecord R1 [...])
> (def R1-fns
> {fn1 (fn ...)})
>
> (defrecord R2 [...])
> (def R2-fns
> {fn2 (fn ...)
> fn3 (fn ...)})
>
> (extend YourProtocol
> R1 (merge defaults R1-fns)
> R2 (merge defaults R2-fns))
>
> Another way is the following macro:
>
> (defmacro defrecord-with-defaults
> [record fields & protocol-default-fns]
> (let [process-protocol
> (fn [[protocol defaults fns]]
> (let [defaults (when defaults
> (->> defaults
> resolve
> var-get
> (map (fn [[k f]]
> (vector
> k (cons (symbol (name k)) (next f)))))
> (into {})))]
> (list* protocol
> (->> fns
> (map #(array-map (-> % first name keyword) %))
> (apply merge defaults)
> (map second)))))
> split-protocols
> (fn split-protocols
> [p-d-fs]
> (lazy-seq
> (when-let [[p d & fs] (seq p-d-fs)]
> (let [[fs next-p-d-fs] (split-with (complement symbol?) fs)]
> (cons [p d fs] (split-protocols next-p-d-fs))))))]
> `(defrecord ~record ~fields
> ~@(mapcat process-protocol (split-protocols protocol-default-fns)))))
>
> Usage:
>
> (def foo-defaults
> `{:bar (fn ([this# that#] nil))
> :baz (fn [this# that#] nil)})
>
> (defrecord-with-defaults R [a b]
> Foo foo-defaults
> (bar [this that] nil)
> Frob nil
> (frobnicator [this] nil))
>
> Note: you have to syntax-quote the functions in the default map (as for
> definline). And you can have only one arity per function. Here the
> corresponding expansion:
>
> (clojure.core/defrecord FooImpl1 [a b]
> Foo
> (bar [this that] nil)
> (baz [this__711__auto__ that__712__auto__] nil)
> Frob
> (frobnicator [this] nil))
>
> Sincerely
> Meikel
>
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--
Antoni Batchelli
- twitter: @tbatchelli , @disclojure
--- email: tbatche...@gmail.com
----- web: tbatchelli.org , disclojure.org
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