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?
My understanding is that if you have (:c b) somewhere in your
code, and "b" is always an object of the same deftype with
a field "c", you're getting Java field-speed access (once hotspot
has done what it does). Yes, that's faster than array map
lookup. It's even faster than struct map accessor function lookup.
> 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, I think that's correct.
> 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?
There will be no shared structure between your two Bar object.
That is, the reference to 2 (or the value 2 itself if it were
a primitive) will be copied to the new object.
> I guess I am just asking if the performance guarantees are those I
> would expect of Clojure (i.e., "too fast" ;-))
This is definitely still too fast. In fact, it keeps getting worse.
--Chouser
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