Hi achim,
That looks like a fine start. Thanks for doing it!
This part concerns me:
> Note: Since clojure maps are no java maps, they can't be equal to java
> maps. This holds for wrapped clojure maps as well - surprisingly (in a
> bad sense), but i don't see a way around this:
>
> (= (doto (HashMap.) (put 1 2)) {1 2})
> -> false
>
> (= (jmap {1 2}) {1 2})
> -> false
Here's my understanding of how = works in Clojure (corrections welcome):
Clojure defines "=" (for all types) as "has the same value". For two
maps A and B (of any concrete type) this means:
For every key in A there exists a key in B that is = to it.
For every key in B there exists a key in A that is = to it.
For every key k in A, the value associated with k in A is = to the
value associated with k in B
The map types that we have now implement this. I think it's very
important that jmap fit in with that definition of "=".
What prevents jmap from participating in this same check? If there are
more changes to existing Clojure code that are necessary to support
this, I think they should be part of a jmap patch.
--Steve
On Sep 29, 2008, at 2:30 PM, Achim Passen wrote:
>
> Hi!
>
> Here's a patch to add java.util.Map support to clojure maps, along
> with some example code. This my first java code in quite some time, so
> if you notice i'm doing anything odd or incorrect, please don't
> hesitate to comment.
>
> http://groups.google.com/group/clojure/web/jmap.diff
> http://groups.google.com/group/clojure/web/jmap-examples.clj
>
> It has been discussed why clojure maps do not implement the
> java.util.Map interface (short version: j.u.Map and j.u.Collection
> clash, Collection being preferrable). This patch provides two
> functions, "jmap" and "cmap", the former to wrap a clojure map in a
> flyweight wrapper that provides the j.u.Map implementations, the
> latter to unwrap it again.
>
> The results of a calls to j.u.Map methods are automatically wrapped
> again if they return maps, so from the java point of view, nested
> clojure maps show up as nested java maps.
>
> From the clojure point of view, wrapped maps retain most of the
> functionality of their unwrapped counterparts: they can be invoked,
> assoced and conjed, etc., the result being a full-featured clojure map
> in each case. However ...
>
> Note: Since clojure maps are no java maps, they can't be equal to java
> maps. This holds for wrapped clojure maps as well - surprisingly (in a
> bad sense), but i don't see a way around this:
>
> (= (doto (HashMap.) (put 1 2)) {1 2})
> -> false
>
> (= (jmap {1 2}) {1 2})
> -> false
>
> Efficiency: lookup key- and mapentry-sets on wrapped maps should be
> fast, since they just delegate calls to the clojure map inside. Lookup
> on the values takes linear time though, and as far as i can see, we
> can't do better, because the values themselves are not structured for
> fast access in clojure maps.
>
> Comments are most welcome!
>
> Kind regards,
> achim
>
> --
> http://rauschabstand.twoday.net
>
> >
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