Thank you for the responses. However, when I look here:
http://clojure.org/multimethods
I see that it says:
"You can define hierarchical relationships with (derive child parent).
Child and parent can be either symbols or keywords, and must be
namespace-qualified"
Is there any way I can establish a hierarchical relationship without it
being name-spaced qualified? I would like to be able to (slingshot/throw+
{:type some-symbol}) and have this be caught in a different namespace, but
I need a way to match the some-symbol, and I would ideally like it if
some-symbol
might be part of a hierarchy, such that I'm matching again some-symbol's
parent.
Is that possible?
I guess I could hard-code all of the namespaces, such that the symbols are
all:
some-namespace/some-symbol
but that does great reduce the flexibility of the system.
On Saturday, August 9, 2014 3:30:33 PM UTC-4, James Reeves wrote:
>
> Jozef is correct, but to give some examples:
>
> (ns example.core
> (:require [example.other :as other]))
>
> (= ::foo :example.core/foo)
> (= ::other/foo :example.other/foo)
>
> (not= :foo :example.core/foo)
> (not= :example.core/foo :example.other/foo)
> (not= :other/foo ::other/foo)
>
> - James
>
>
>
> On 9 August 2014 19:14, Jozef Wagner <jozef....@gmail.com <javascript:>>
> wrote:
>
>> Keep in mind that :: is just a syntax sugar that is processed by the
>> reader, before the compiler kicks in. ::foo is a shorthand for
>> :your.current.ns/foo. Its purpose is to make it easy to create keywords
>> that do not clash with other ones.
>>
>> Keywords are equal (and identical) only when both of their namespaces and
>> names are equal. :ns1/foo is thus not equal to :ns2/foo, nor to just :foo.
>> ::
>> is used in cases where you want to exploit this important property of
>> keywords, so that your keyword won't e.g. clash with other keywords in a
>> collection, contents of which you don't know.
>>
>> Jozef
>>
>>
>> On Saturday, August 9, 2014 7:46:45 PM UTC+2, larry google groups wrote:
>>>
>>> Please forgive this stupid question, but I'm still trying to understand
>>> exactly what the double "::" means. I have read that I can use (derive) to
>>> establish a hierarchy and I can imagine how this would be useful for things
>>> like throwing errors and catching them and logging, but I've also read that
>>> "::" adds the namespace to the symbol, so I would assume that I can not
>>> match ::logging from one namespace with ::logging from another?
>>>
>>> I'm thinking of this especially in my use of Slingshot, where I was
>>> thinking of doing something like:
>>>
>>> (throw+ {:type ::database-problem :message "something wrong in the
>>> database query"})
>>>
>>> and then at a higher level in my code I was going to catch it with
>>> something like:
>>>
>>> (derive ::database-problem ::logging)
>>>
>>> and then using Dire:
>>>
>>> (dire/with-handler! #'database/remove-this-item
>>> [:type ::logging]
>>> (fn [e & args]
>>> (timbre/log (str " database/remove-this-item: The time : "
>>> (dates/current-time-as-string) ( str e))))
>>>
>>> but conceptually I am having trouble understanding how ::logging in one
>>> namespace can match ::logging in another namespace. Perhaps I should just
>>> use normal keywords?
>>>
>>>
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