On Thu, 8 Nov 2018 at 14:36, alex <fmno...@gmail.com> wrote:
> No, that will not work exactly like Ruby eigenclass, cause eigenclass has
> a priority when method lookup is performed. In Clojure case if instance's
> class has implementation of method, it will be preferred instead of meta
> version. If I understand everything correctly.
>
Yes, clearly it'll not be exactly like Ruby eigenclasses; because this is
clojure! :-) My point was really that it's spiritually similar if you
consider them as a means of extending individual instances you're given
with new functionality. Though yes, thankfully you can't use this for
monkey patching over existing functionality; but who would want to do
that?! ;-)
R.
>
> четверг, 8 ноября 2018 г., 12:33:10 UTC+2 пользователь Rick Moynihan
> написал:
>>
>> Cool, so I guess it's the clojure of equivalent of Ruby's eigenclasses:
>>
>> f = "some object"
>> class << f
>> def foo
>> "new foo method on f"
>> end
>> end
>>
>> f.foo # => "new foo method on f"
>>
>> It's a shame this mechanism only works for values implementing IMeta, but
>> I understand the JVM is a little prohibitive in this regard.
>>
>> Even so I suppose the main use of this is that it lets a caller give you
>> a value, and you can return a plussed up version with new capabilities,
>> without having to return a wrapped value. Wrapped values are sometimes
>> problematic because they introduce new representations of existing types,
>> and this allows an API to return values to the caller that behave the same
>> as what went in. Neat!
>>
>> R.
>>
>> On Tue, 6 Nov 2018 at 15:51, Alex Miller <al...@puredanger.com> wrote:
>>
>>>
>>> On Tuesday, November 6, 2018 at 9:25:31 AM UTC-6, John Schmidt wrote:
>>>>
>>>> Nice to see continued progress on Clojure 1.10!
>>>>
>>>> It is not clear to me what metadata extension provides that is not
>>>> already possible with direct definitions or external extensions. Some
>>>> additional background or a small motivating example would be much
>>>> appreciated in clearing up the confusion!
>>>>
>>>
>>> Metadata extension allows you to implement protocols on a per-value
>>> basis (the others are type/class-oriented). This opens up a whole new range
>>> of potential uses for protocols. Rich was already using this approach for
>>> the new datafy/nav functionality - this made it generic for all protocols.
>>>
>>> Any collection instance can carry metadata, so you can take any
>>> collection instance and dynamically extend a protocol to it by adding
>>> metadata. So if you think about something like Component, which has a
>>> Lifecycle protocol for start/stop, you can now make lightweight components
>>> without needing to make a type or reify:
>>>
>>> $ clj -Sdeps '{:deps {org.clojure/clojure {:mvn/version
>>> "1.10.0-beta5"}, com.stuartsierra/component {:mvn/version "0.3.2"}}}'
>>> Clojure 1.10.0-beta5
>>> user=> (require '[com.stuartsierra.component :as component])
>>> nil
>>> user=> (def c (with-meta {:state :init}
>>> {`component/start (fn [c] (assoc c :state :started))
>>> `component/stop (fn [c] (assoc c :state :stopped))}))
>>> #'user/c
>>> user=> (component/start c)
>>> {:state :started}
>>> user=> (component/stop c)
>>> {:state :stopped}
>>>
>>>
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