Nope, you're right, I missed the "extend, extend-type, extend-protocol"
part of the original post.
On Thu, Nov 8, 2018 at 10:12 AM Alex Miller <a...@puredanger.com> wrote:
>
> On Thursday, November 8, 2018 at 10:44:34 AM UTC-6, tbc++ wrote:
>>
>> The instance based polymorphism is a bit wonky in some cases. Can we get
>> some sort of spec that tells us what the rules are for resolution?
>>
>
> From the top of the thread: "Protocol implementations are checked first
> for direct definitions (defrecord, deftype, reify), then metadata
> definitions, then external extensions (extend, extend-type,
> extend-protocol)." Was that unclear in some way? I think it explains
> everything you're seeing.
>
> We do plan to update the protocols reference page for final release, but
> waiting on that.
>
> We are still doing performance eval on this too - still might change a bit
> more.
>
>
>
>
>> See these cases where it breaks in some rather strange ways.
>>
>> Clojure 1.10.0-beta5
>> user=> (defprotocol ILevel (level [this]))
>> ILevel
>> user=> (extend-protocol ILevel
>> clojure.lang.IPersistentVector
>> (level [this] "interface"))
>> nil
>> user=> (extend-protocol ILevel
>> Object
>> (level [this] "object"))
>> nil
>> user=> (level [])
>> "interface"
>> user=> (level :key)
>> "object"
>> user=> (level (with-meta 'foo {`level (fn [this] "instance")}))
>> "instance"
>> user=> (level (with-meta [] {`level (fn [this] "instance")}))
>> "instance"
>> user=> (defrecord MyType [] ILevel (level [this] "type"))
>> user.MyType
>> ;; Fails to override
>> user=> (level (with-meta (->MyType) {`level (fn [this] "instance")}))
>> "type"
>> user=> (defrecord MyType3 [])
>> user.MyType3
>> user=> (extend-protocol ILevel
>> MyType3
>> (level [this] "type"))
>> nil
>> user=> (level (->MyType3))
>> "type"
>> ;; Overrides
>> user=> (level (with-meta (->MyType3) {`level (fn [this] "instance")}))
>> "instance"
>> user=>
>>
>> So it looks like if someone uses inline protocol extension that class
>> cannot participate in instance level polymorphism. If however they use
>> extend on the type after it's defined then the behavior changes and
>> instance polymorphism is supported.
>>
>>
>> --
> 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
> ---
> 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+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.
>
--
“One of the main causes of the fall of the Roman Empire was that–lacking
zero–they had no way to indicate successful termination of their C
programs.”
(Robert Firth)
--
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
---
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+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
