Re: Trait-like behavior with Protocols
On 9 Feb 2010, at 22:29, aria42 wrote: If this situation is common enough, shouldn't defprotocol support optional implementations which are implicitly merged? Yes, if it is common enough. It's perhaps too early to decide. Konrad. -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@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+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Trait-like behavior with Protocols
If this situation is common enough, shouldn't defprotocol support optional implementations which are implicitly merged? On Feb 9, 6:01 am, Konrad Hinsen wrote: > On 09.02.2010, at 02:14, Stuart Sierra wrote: > > > On Feb 8, 6:13 pm, aria42 wrote: > >> (defprotocol Span > >> (start [self]) > >> (stop [self]) > >> (span-length [self])) > > >> Now I know I can just make span-length a function on Span as opposed > >> to part of the protocol. Is that what one should do? > > > Yes. > > I would say "it depends". > > I have a similar situation in my multiarray package > (http://code.google.com/p/clj-multiarray/). In the multiarray protocol, I > have two functions, "shape" and "rank", with the latter being by definition > the same as (comp count shape). However, I still have "rank" in the protocol, > because for some implementations it is more efficient to compute the rank > directly, rather than construct a shape vector just for computing its length > afterwards. > > In such situations it is useful to provide a default implementation and leave > it up to each type to implement a more efficient alternative or not. With > extend and the maps that go with it, this is easy to achieve: make a map with > the default implementations, and merge this with the type-specific > implementations fed to extend. > > Konrad. -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@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+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Trait-like behavior with Protocols
On 09.02.2010, at 02:14, Stuart Sierra wrote: > On Feb 8, 6:13 pm, aria42 wrote: >> (defprotocol Span >> (start [self]) >> (stop [self]) >> (span-length [self])) >> >> Now I know I can just make span-length a function on Span as opposed >> to part of the protocol. Is that what one should do? > > Yes. I would say "it depends". I have a similar situation in my multiarray package (http://code.google.com/p/clj-multiarray/). In the multiarray protocol, I have two functions, "shape" and "rank", with the latter being by definition the same as (comp count shape). However, I still have "rank" in the protocol, because for some implementations it is more efficient to compute the rank directly, rather than construct a shape vector just for computing its length afterwards. In such situations it is useful to provide a default implementation and leave it up to each type to implement a more efficient alternative or not. With extend and the maps that go with it, this is easy to achieve: make a map with the default implementations, and merge this with the type-specific implementations fed to extend. Konrad. -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@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+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Trait-like behavior with Protocols
I think the extend function is made exactly to support the concrete implementation of protocols. It takes a type, and then any number of protocol + function map pairs, where keyword names map to functions. Checkout the protocol docs on assembla and look for extend: http://www.assembla.com/wiki/show/clojure/Protocols or read a recent post by Rich where he talks about some of the design decisions behind these constructs: http://groups.google.com/group/clojure/msg/330c230e8dc857a9 -Jeff Rose On Feb 9, 12:13 am, aria42 wrote: > Is it possible to have default implementations associated with > functions in a protocol? This is most useful when some protocol > functions are defined in terms of other. For instance, > > (defprotocol Span > (start [self]) > (stop [self]) > (span-length [self])) > > Now I know I can just make span-length a function on Span as opposed > to part of the protocol. Is that what one should do? -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@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+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Trait-like behavior with Protocols
Hi,
On Feb 9, 12:13 am, aria42 wrote:
> Is it possible to have default implementations associated with
> functions in a protocol? This is most useful when some protocol
> functions are defined in terms of other. For instance,
>
> (defprotocol Span
> (start [self])
> (stop [self])
> (span-length [self]))
>
> Now I know I can just make span-length a function on Span as opposed
> to part of the protocol. Is that what one should do?
The last time I checked, it was my understanding the mix-ins are used
for this.
(defprotocol Thing (abc []) (xyz []))
(def AThing {:abc (fn [] ...) :xyz (fn [] )})
(deftype Banana ...)
(extend Thing Banana (merge AThing {:abc (fn []...)}))
This would effectively use the "default" implementation of xyz and
provide a custom one for xyz.
But I'm not up-to-date with the protocol stuff.
Sincerely
Meikel
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Re: Trait-like behavior with Protocols
On Feb 8, 2010, at 6:13 PM, aria42 wrote: > Is it possible to have default implementations associated with > functions in a protocol? This is most useful when some protocol > functions are defined in terms of other. For instance, > > (defprotocol Span > (start [self]) > (stop [self]) > (span-length [self])) > > Now I know I can just make span-length a function on Span as opposed > to part of the protocol. Is that what one should do? Can you show me what this looks like? Thanks, Dan -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@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+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Trait-like behavior with Protocols
On Feb 8, 6:13 pm, aria42 wrote: > (defprotocol Span > (start [self]) > (stop [self]) > (span-length [self])) > > Now I know I can just make span-length a function on Span as opposed > to part of the protocol. Is that what one should do? Yes. -SS -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@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+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Trait-like behavior with Protocols
Is it possible to have default implementations associated with functions in a protocol? This is most useful when some protocol functions are defined in terms of other. For instance, (defprotocol Span (start [self]) (stop [self]) (span-length [self])) Now I know I can just make span-length a function on Span as opposed to part of the protocol. Is that what one should do? -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@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+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
