On Thu, Nov 19, 2009 at 12:39 PM, Krukow <karl.kru...@gmail.com> wrote:
> On Nov 19, 12:01 am, samppi <rbysam...@gmail.com> wrote:
>> Question: are the general mechanisms for accessing and setting fields
>> their keywords and assoc respectively:
>> (deftype Bar [a b c d e])
>> (def b (Bar 1 2 3 4 5))
>> (:c b)
>> (def c (assoc b :e 2))
>> Does (:c b) and (assoc b :e 2) take advantage of Bar's field
>> information? Is it any faster than using an array map? Are there any
>> equivalents to struct maps' accessor functions?
>
> I've been wondering about this myself. I think you'd often want a
> "persistent" types in the sense of the persistent datastructure.
>
> You can use the ability to implement interfaces, specifically
> automatic support for IPersistentMap:
>
> ser=> (deftype Bar [a b] [clojure.lang.IPersistentMap])
> #'user/Bar
> user=> (assoc (Bar 1 2) :a 42)
> #:Bar{:a 42, :b 2}
> user=>
>
> I have a question here, though: what is this?
>
> ser=> (assoc (Bar 1 2) :c 42)
> #:Bar{:a 1, :b 2, :c 42}
> user=> #:Bar{:a 1, :b 2, :c 42}
>
> Is it a "Bar" with field-speed access to :a and :b and map-speed
> access to :c?
Yes.
>
> Also can I assume that
>
> (assoc (Bar 1 2) :a 42)
> #:Bar{:a 42, :b 2}
>
> will share structure with the (Bar 1 2) and still has fast access
> to :a? Is the assoc function using that :a is a field?
>
Shared structure only kicks in when data structures become large
enough for it to be a performance advantage. That's not the case for
small maps or the fixed fields of a deftype.
> I guess I am just asking if the performance guarantees are those I
> would expect of Clojure (i.e., "too fast" ;-))
>
Yup. The fixed field access to deftypes via keyword literal lookup is
the fastest offered by any Clojure data structure.
Rich
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