On 22 August 2017 at 23:04, Timothy Baldridge <[email protected]> wrote:
> I find the arguments for variants very unconvincing. As you stated with
> specs and s/keys you can spec the same sort of data, and in a way that's
> much more open-ended.
>
> For example:
>
> [:person {:name "Tim" :grade "B"}]
>
> What is the type of this data? We would probably guess a :person. But what
> if we wanted to "cast" it to a :student? Well then we'd have to change the
> variant tag to :student, but then it would no longer be a person, unless we
> introduced some sort of inheritance that said all students are people.
>
I don't think that example is a representative use of variants in Clojure.
More typically, variants are used like key/value pairings that exist
outside a map. For example:
[:person/name "Tim"]
If you actually have a map, the key/value pairs speak for themselves:
#:person{:name "Tim", :grade "B"}
We can tell this is a "person" because it adheres to a particular shape,
which can be specced out:
(s/def :person/student (s/keys :req [:person/name :person/grade]))
But if you just have a key/value pairing, the value alone doesn't tell you
much:
"Tim"
Using a vector to represent a key/value seems to fit in well with how
Clojure currently works:
(find m :person/name)
=> [:person/name "Tim"]
But there's no "s/variant" or "s/entry" spec that's as convenient to use as
s/keys.
--
James Reeves
booleanknot.com
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