Ya, I guess the article says that some DSL uses them, like hiccup, so maybe
its only in the perspective of a DSL you'd need to parse, and not really
for modeling business entities.
Like this:
(s/def ::temp (s/or :one string?
:two int?))
Will conform to a variant:
=> (s/conform ::temp "one-two")
[:one "one-two"]
=> (s/conform ::temp 12)
[:two 12]
And not to a tagged record like:
{:tag :one
:val "one-two"}
But, I don't know, that seems like a different and uncommon use case, I
don't really see this as using a sum type, just describing data to be
parsed, which I guess the vector form can be easier to work with. I think
the clojurescript AST is actually using tagged records, and most people
find it too verbose because of it.
Anyways, I'd still like to hear if there's a major benefit I'm overseeing,
or a detail I'm not understanding, if any.
P.S.: I figured the difference between (s/or) and (s/multi-spec) I think.
S/or is like structural-types, my example actually doesn't work, because
:filename and :url have the same structure, both string? So conform will
not be able to tell them apart. So if you need to know any kind of semantic
difference which the shape can not infer, (s/or) won't work, you'll need
(s/multi-spec) instead, which are more like nominal-types. Multi-spec I
guess can also use any function to select the appropriate spec, so they're
more powerful, but often I think the way I'm using it will be most common.
On Tuesday, 22 August 2017 18:00:21 UTC-7, tbc++ wrote:
>
> I think the article is a bit misleading. Variants were never that popular
> in Clojure. Infact I've never seen them used in production code or the most
> common Clojure libraries. So I'm a bit perplexed as to why the article
> recommends them so strongly.
>
> So I think the answer is, they are a fun thought experiment in Clojure,
> but are of limited usefulness due to the tools we have available that make
> them unneeded.
>
> It's a bit like recommending that new users use actors in Clojure. Sure,
> you can shoehorn them in, but there's a reason why they aren't the default.
> --
> “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)
>
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