It occurs to me that this can be simplified by using defrecord in place of
deftype. We can eliminate the Composite interface, because compositeMap
becomes the identity function. The code now becomes:
(def blip [this x y z] ((:blip this) this x y z))
(defprotocol gran
(blip this x y z))
(defrecord wackel)
(defn new-wackel [opts] (assoc opts :blip (fn [this x y z] (+ x y z)))
(extend wackel
gran
{:blip blip})
This is better, but still a bit to swallow. Also, note I fixed a bug in
new-wackel.
On Tue, Nov 24, 2015 at 9:37 AM, William la Forge <laforg...@gmail.com>
wrote:
> So lets look at some artifacts then. I think we need an interface that all
> composites implement:
>
> (definterface Composite
> (compositeMap []))
>
> The function composite-map returns the map which holds the aggregated
> functions and data.
>
> Now lets look at a sample function, blip:
>
> (def blip [^Composite this x y z] ((:blip (.compositeMap this)) this x y
> z))
>
> and a protocol that includes blip:
>
> (defprotocol gran
> (blip ^Composite this x y z))
>
> Next we define a type which will hold an aggregate that includes an
> implementation of blip:
>
> (deftype wackel [my-map]
> Composite
> (defn compositeMap [_] my-map))
>
> and a function to create an instance of that type:
>
> (defn new-wackel [this opts] (assoc opts :blip (fn [this x y z] (+ x y z)))
>
> Finally, we can extend our type with the protocol:
>
> (extend wackel
> gran
> {:blip blip})
>
> I find this uncomfortable. In Rich's terms this is simple but hard. To be
> expected, as it is a major decomplection. But it will take me a while to
> get comfortable with this. :-(
>
> --b
>
>
>
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