On Wed, Apr 10, 2013 at 2:13 PM, Jim foo.bar <jimpil1...@gmail.com> wrote:
> On 10/04/13 14:03, Simon Katz wrote:
>
>> Second, Clojure supports namespace-qualified keywords, presumably because
>> it's possible that different libraries might want to use the same keyword
>> for different purposes.
>>
>
> I don't think that is the reason for having namespace-qualified
> keywords...different libraries might want to use the same keyword for
> different purposes and that is fine - no clashes (or at elast I've not
> understood what you mean).
>
> It's my understanding that ::foo has (or should have) actual 'meaning' in
> whatever namespace it exists whereas :foo doesn’t really have any 'meaning'.
>
Here's an example of what I mean. In the code below, a/foo and b/bar use
unqualified keywords. At the line marked (1), which uses both those
functions, you can see that the value set up by b/bar has been lost.
Similarly, at (2) the value set up by a/foo has been lost. (1) and (2)
illustrate what I mean by a clash.
At (3), which uses functions that use namespace-qualified keywords, the
result includes the values set up by both a/foo-nsq and b/bar-nsq — no
clash.
Hopefully that clarifies things.
I don't think I'm trying to do anything unusual here. For example, *The
Joy of Clojure* (pages 69-72) and *Clojure Programming* (page 14) both talk
about using namespace-qualified symbols in this kind of way.
user> (ns a)
a> (defn foo [m] (assoc m :kw 1))
a> (defn foo-nsq [m] (assoc m ::kw 1))
a> (ns b)
b> (defn bar [m] (assoc m :kw 2))
b> (defn bar-nsq [m] (assoc m ::kw 2))
b> (in-ns 'user)
user> (a/foo (b/bar {})) ; (1)
;; => {:kw 1}
user> (b/bar (a/foo {})) ; (2)
;; => {:kw 2}
user> (a/foo-nsq (b/bar-nsq {})) ; (3)
;; => {:a/kw 1, :b/kw 2}
It seems to me odd that Clojure recognises that namespace-qualified symbols
are needed and yet that defrecord seems to not respect the fact.
I don't really think you want to access your record fields with a
> namespace-qualified keyword, do you? How would that work exactly? what if
> you got an instance of the record outside the namespace where the
> namespace-qualified keyword is defined? It doesn't make sense to me at
> all...
I don't understand this. (It's possible to use a namespace-qualified
symbol from outside the namespace.)
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