> Keywords hierarchies need to be namespace qualified, but you can require > namespaces and use the alias, as I demonstrated in my earlier example.
I wasn't thinking clearly about what this meant, but now I see what you mean. I could potentially have all of my (derive) statements in one namespace, define the keywords there, and then any namespace that will use those keywords can require that namespace and use those keywords. Thank you for your help. On Saturday, August 9, 2014 4:02:59 PM UTC-4, James Reeves wrote: > > Keywords hierarchies need to be namespace qualified, but you can require > namespaces and use the alias, as I demonstrated in my earlier example. > > To give a further example, suppose you have a namespace like: > > (ns example.other) > > (derive ::dog ::animal) > (derive ::cat ::animal) > > (defmulti speak identity) > > If you require this namespace, you can use the alias instead of the fully > qualified name in keywords: > > (ns example.core > (require [example.other :as o])) > > (defmethod o/speak ::o/dog [_] "bark") > (defmethod o/speak ::o/cat [_] "meow") > > - James > > > On 9 August 2014 20:49, larry google groups <lawrenc...@gmail.com > <javascript:>> wrote: > >> 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> 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? >>>>> >>>>> >>>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "Clojure" group. >>>> To post to this group, send email to clo...@googlegroups.com >>>> >>>> Note that posts from new members are moderated - please be patient with >>>> your first post. >>>> To unsubscribe from this group, send email to >>>> clojure+u...@googlegroups.com >>>> >>>> For more options, visit this group at >>>> http://groups.google.com/group/clojure?hl=en >>>> --- >>>> You received this message because you are subscribed to the Google >>>> Groups "Clojure" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to clojure+u...@googlegroups.com. >>>> >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> >>> > -- You received this message because you are subscribed to the Google Groups "Clojure" group. 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