On Thursday, February 22, 2018 at 12:58:00 AM UTC+1, Sean Corfield wrote:
> Looking around I see lots of cases where people do use conformers for
> That doesn’t make them right 😊
Oh, I agree, I'm just being realistic. The cat is out of the bag. I just
googled for 's/conformer' and found an entire library of conformers that do
various data conversions.
> At a first glance it seems very natural, and warnings not to do it are not
> easily found.
> Every single time coercion comes up anywhere in the context of spec,
> someone says “don’t do that”, and they’ve been saying it since the earliest
> alpha versions of spec. You would be correct to point out that nothing in
> the spec overview or spec guide on clojure.org carries this caution,
> however (and I think it’s a reasonable “ask” for the guide to be updated to
> include such a caution).
> My recommendation is to have a strictly non-coercive spec for the target
> data “type” / shape you want, and to have a second spec that combines the
> coercion you want with that spec. That way you have a way to tell if your
> uncoerced data conforms to the spec, as well as a way to do coercion in
> s/conform. They are – and should be – two separate specs and two separate
> operations. They represent different layers of abstraction inside your
> application (so “of course” they should be two separate specs, one built on
> top of the other).
Also agree. I think coercion and conformance verification are two separate
concepts and should not be conflated. I like the idea with two specs, as
this lets me get some reuse.
> Given that the overview and the guide don’t even mention s/conformer, I’m
> not sure where that recommendation should live. Alex, any thoughts on this,
> since you seem to be the one most often making the recommendation?
As a spec user, I would expect to learn about this from the spec guide.
Also, I still believe that in the short term a function that validates a
spec without calling conformers would be useful.
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