Re: (type ...) vs (class ...)
I think the main intention of type is to be used as a more generic version
of class, that lets clojure data participate alongside java objects etc
with multi-methods etc.
i.e.
(defmulti foo type)
(defmethod foo java.lang.String [x]
:string-dispatched)
(defmethod foo :my-clojure-type [x]
:my-clojure-type-dispatched)
(foo ^{:type :my-clojure-type} {:blah :blah}) ;; =>
:my-clojure-type-dispatched
derive et al also let you use keywords to augment java class hierarchies
with new types, provide multiple inheritance and priorities with
prefer-method etc.
R.
On Fri, 12 Feb 2016 at 21:37, Alan Thompson wrote:
> Hey - Just saw something on the clojure.core/type function:
>
>
>
> (defn type
> "Returns the :type metadata of x, or its Class if none"
> {:added "1.0"
> :static true}
> [x]
> (or (get (meta x) :type) (class x)))
>
>
> I have never seen this before, and it appears the :type metadata is not
> used in the clojure.core source code itself. Is this ever used for
> anything or is it just a vestigial remnant from long ago?
>
> Alan
>
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Re: (type ...) vs (class ...)
Found this: https://groups.google.com/forum/#!searchin/clojure/%22type$20metadata%22%7Csort:date/clojure/LBGsPs2__pQ/oLgx_kgmQxgJ :tag is applied to source forms to communicate type hints to the compiler. :type can be used, by convention, to add 'type names' to runtime data structures that support metadata. The type function will return the :type metadata if present, else the class, making it a handy dispatch function. Neither :tag nor :type are used directly by isa? Rich On Wednesday, October 24, 2018 at 12:30:14 AM UTC-7, Didier wrote: > > Reviving this thread, as I'd like to kmow if someone can explain the > purpose of the type metadata and what is responsible for adding it? -- 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.
Re: (type ...) vs (class ...)
the type function in clojure.core lets you override the nominal class of an
object with the :type metadata
user=> (type {})
clojure.lang.PersistentArrayMap
user=> (type ^{:type :foo} {})
:foo
On Wed, Oct 24, 2018 at 9:41 AM alex wrote:
> Looks like pre defrecord stuff used in early days to add "type" to map.
> Can still be used if you need "type" on a map without using defrecord.
>
> среда, 24 октября 2018 г., 10:30:14 UTC+3 пользователь Didier написал:
>
>> Reviving this thread, as I'd like to kmow if someone can explain the
>> purpose of the type metadata and what is responsible for adding it?
>
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Re: (type ...) vs (class ...)
Looks like pre defrecord stuff used in early days to add "type" to map. Can still be used if you need "type" on a map without using defrecord. среда, 24 октября 2018 г., 10:30:14 UTC+3 пользователь Didier написал: > > Reviving this thread, as I'd like to kmow if someone can explain the > purpose of the type metadata and what is responsible for adding it? -- 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.
Re: (type ...) vs (class ...)
Reviving this thread, as I'd like to kmow if someone can explain the purpose of the type metadata and what is responsible for adding it? -- 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.
Re: (type ...) vs (class ...)
On 02/12/2016 01:37 PM, Alan Thompson wrote:
> Hey - Just saw something on the clojure.core/type function:
>
>
>
> (defn type
> "Returns the :type metadata of x, or its Class if none"
> {:added "1.0"
> :static true}
> [x]
> (or (get (meta x) :type) (class x)))
>
>
>
> I have never seen this before, and it appears the :type metadata is not
> used in the clojure.core source code itself. Is this ever used for
> anything or is it just a vestigial remnant from long ago?
>
> Alan
It is used by the printing system (see core_print.clj). If I write a
multimethod that is dispatching on type/class whatever, `type` is the
first function I reach for.
>
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And what is good, Phaedrus,
And what is not good—
Need we ask anyone to tell us these things?
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Re: (type ...) vs (class ...)
On 02/12/2016 01:47 PM, Kevin Downey wrote:
> On 02/12/2016 01:37 PM, Alan Thompson wrote:
>> Hey - Just saw something on the clojure.core/type function:
>>
>>
>>
>> (defn type
>> "Returns the :type metadata of x, or its Class if none"
>> {:added "1.0"
>> :static true}
>> [x]
>> (or (get (meta x) :type) (class x)))
>>
>>
>>
>> I have never seen this before, and it appears the :type metadata is not
>> used in the clojure.core source code itself. Is this ever used for
>> anything or is it just a vestigial remnant from long ago?
>>
>> Alan
>
> It is used by the printing system (see core_print.clj). If I write a
> multimethod that is dispatching on type/class whatever, `type` is the
> first function I reach for.
Oh, my mistake, print-method actually re-implements `type`, with the
added restriction that is has to be a keyword.
>
>>
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>
>
--
And what is good, Phaedrus,
And what is not good—
Need we ask anyone to tell us these things?
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