Hi.
Spec-tools (https://github.com/metosin/spec-tools) has some tools for this:
the spec visitor (walking over all core specs, e.g. to collect all
registered specs) and map-conformers: fail-on-extra-keys and
strip-extra-keys.
Here's an example to strip away extra keys:
(require '[clojure.spec.alpha :as s])
(require '[spec-tools.core :as st])
(s/def ::name string?)
(s/def ::street string?)
(s/def ::address (st/spec (s/keys :req-un [::street])))
(s/def ::user (st/spec (s/keys :req-un [::name ::address])))
(def inkeri
{:name "Inkeri"
:age 102
:address {:street "Satamakatu"
:city "Tampere"}})
(st/select-spec ::user inkeri); {:name "Inkeri"; :address {:street
"Satamakatu"}}
There is CLJ-2116 that would enable this without any wrapping of specs:
https://dev.clojure.org/jira/browse/CLJ-2116. Seems stalled.
If runtime transformations would be supported (currently: out of scope), I
think we could go even further - we could rewrite conform* as walk* to
support all of fast coercion, explain and conform. We are using conform +
unform as a substitute of coercion but sadly, it's quite slow, especially
for maps.
Tommi
tiistai 3. lokakuuta 2017 16.10.30 UTC+3 Yuri Govorushchenko kirjoitti:
>
> 1) About `s/keys` silently ignoring missing value specs. My question was:
> "Is there any way to ensure that the keys I used in `s/keys` have the
> associated specs defined?."
>
> Specs can be defined or added later, so there is no valid way to do this.
>
>
> OK, so requiring that values are spec-ed can't be enforced at compilation
> time because this would make it impossible to define value specs after
> `s/keys`:
>
> ```
> (s/def ::foo (s/keys :req [::bar]))
> ,,,
> (s/def ::bar ,,,)
> ```
>
> This can explain why it's not built into the library. In such case I'm
> fine with using a custom macro instead of `s/keys` (see my gist in the
> previous post).
>
> But what about enforcing existence of value specs at runtime, during
> validation? `s/cat` does that, e.g.:
>
> ```
> cljs.user=> (s/def ::foo (s/cat :bar ::baz))
> :cljs.user/foo
> cljs.user=> (s/valid? ::foo [123])
> Unable to resolve spec: :cljs.user/baz
> ```
>
> Why is it then not a default behaviour for `s/keys` as well? I.e.:
>
> ```
> ; current behavior
> cljs.user=> (s/def ::foo (s/keys :req [::x]))
> :cljs.user/foo
> cljs.user=> (s/valid? ::foo {::x 123})
> true
>
> ; desired behavior
> cljs.user=> (s/def ::foo (s/keys :req [::x]))
> :cljs.user/foo
> cljs.user=> (s/valid? ::foo {::x 123})
> Unable to resolve spec: :cljs.user/x
> ```
>
> I don't think Spec-ulation Keynote addresses this behaviour.
>
> 2) There's no *built-in* way restrict the keyset of the map in `core.spec`.
>
> The reasoning for this seems to be based around the idea of backwards
> compatible evolving specs (see Spec-alution Keynote). But there are several
> good examples already covered in this thread which demonstrate that it
> would be very convenient to also have strict keyset validations available
> in `core.spec`. After all, the library is about specifying the structure of
> data and not only about specifying API contracts.
>
> 3) Thinking more about `s/keys` vs. `s/cat` *specifically* in the context
> of asserting API contracts (I'm stressing on the context here because
> `core.spec` is a general library and should take in account other use cases
> too).
>
> In this context it's even more apparent that `s/keys` should behave in the
> same way as `s/cat` because there's not much difference between positional
> arguments and keyword arguments. I'll try to illustrate what I mean with an
> example. Let's say there's a function with positional arguments:
>
> ```
> (defn foo-pos [x y z])
>
> ; call example:
> (foo xxx yyy zzz)
> ```
>
> I hope we can agree that it's more or less equivalent to this function
> with the keyword arguments where each keyword corresponds to the position
> number in `foo-pos`:
>
> ```
> (defn foo-pos* [{x 1 y 2 z 3}])
>
> ; call example:
> (foo-pos* {1 xxx 2 yyy 3 zzz})
> ```
>
> And making a step further to better naming:
>
> ```
> (defn foo-kw [{:keys [::x ::y ::z]}])
>
> ; call example:
> (foo-kw {::x xxx ::y yyy ::z zzz})
> ```
>
> So, the biggest difference is the syntax of function calls. Keyword
> arguments are usually more readable (esp. when there are several args) and
> easier to maintain (since they can be reordered at the call site and
> function definition safely). Let's now spec-ify the arguments using `s/cat`
> for positional args and `s/keys` for keyword args (as recommended in docs).
> These specs ensure that argument `x` is present and is of type `::x`, `y`
> is present and is of type `::y`, etc.:
>
> ```
> (s/def ::foo-pos-args (s/cat :x ::x :y ::y :z ::z))
> (s/def ::foo-kw-args (s/keys :req [::x ::y ::z]))
> ```
>
> Now (because the functions are equivalent) I'd expect their specs to
> validate equivalent inputs in the similar way. But it's not the case if
> developer forgets to define the `::y` spec!
>
> ```
> ; ::y spec is missing
> (s/def ::x int?)
> (s/def ::z int?)
>
> ; positional args
> (def pos-inputs [1 2 3])
> (s/valid? ::foo-pos-args pos-inputs) ; => Unable to resolve spec:
> :cljs.user/y (good)
>
> ; keyword args
> (def kw-inputs {::x 1 ::y 2 ::z 3})
> (s/valid? ::foo-kw-args kw-inputs) ; => true (ouch!)
> ```
>
> TL/DR: (specifically in the context of function contracts) `core.spec`
> shouldn't treat APIs with positional arguments and APIs with keyword
> arguments differently and thus `s/keys` should check arg values at keys in
> the same way `s/cat` checks arg values at positions.
>
> On Tuesday, October 3, 2017 at 6:01:06 AM UTC+3, Alex Miller wrote:
>>
>>
>>
>> On Monday, October 2, 2017 at 10:37:31 AM UTC-5, Yuri Govorushchenko
>> wrote:
>>>
>>> Hi!
>>>
>>> I have some noobie questions for which I couldn't google the compelling
>>> answers.
>>>
>>> 1) Is there any way to ensure that the keys I used in `s/keys` have the
>>> associated specs defined?
>>>
>>
>> Specs can be defined or added later, so there is no valid way to do this.
>>
>>
>>> At compile time or at least at runtime. Maybe via an additional library?
>>> I could imagine a macro (smt. like `s/keys-strict` or `s/map-pairs`, as
>>> maps can also be viewed as sets of spec'ed pairs) which additionally checks
>>> that all keys have specs registered. I'm OK with sacrificing some
>>> flexibility (e.g. being able to define key specs after map specs,
>>> dynamically, etc.) in favour of more strictness.
>>>
>>> Motivation: I don't fully trust my map validation code when using
>>> `core.spec`. `s/keys` doesn't require that the key has the spec registered
>>> to validate its value. Although this may be flexible but in practice can
>>> lead to errors. Specifically, it's quite easy to forget to create a spec
>>> for a key, mistype it or forget to require the namespace in which key spec
>>> is defined (e.g. if the common key specs reside in a dedicated ns):
>>>
>>> ```
>>> ; totally forgot to define a spec for ::foo
>>> (s/def ::bar (s/keys :req [::foo]))
>>>
>>> ; fooo vs. foo typo
>>> (s/def ::fooo string?)
>>> (s/def ::bar (s/keys :req [::foo]))
>>>
>>> ; :common/foo vs. ::common/foo typo
>>> (s/def ::bar (s/keys :req [:common/foo]))
>>>
>>> ; didn't require common.core ns (spec for :common.core/foo is not added
>>> to global registry)
>>> (s/def ::bar (s/keys :req [:common.core/foo]))
>>> ```
>>>
>>> These subtle mistakes can lead to map validations passing silently (as
>>> long as keysets are correct).
>>>
>>> Related to this: there're feature requests for Cursive IDE which try to
>>> address typing and reading mistakes related to keywords, e.g.
>>> https://github.com/cursive-ide/cursive/issues/1846 and
>>> https://github.com/cursive-ide/cursive/issues/1864.
>>>
>>> After using Schema for a while it's difficult to appreciate the way
>>> `core.spec` defines it's own global registry which uses keywords instead of
>>> using spec instances and good old variables, especially since Cursive IDE
>>> has quite a nice support for variables already. But I think this is another
>>> topic which was already discussed, e.g. in
>>> https://groups.google.com/forum/#!topic/clojure/4jhSCZaFQFY ("Spec
>>> without global registry?").
>>>
>>> 2) What is the motivation for library having a "loose" default behaviour
>>> of `s/keys` and no "strict" variant at all for spec-ing both keys and
>>> values at the same tome? I think in majority of cases I'd need to spec both
>>> keys and values of the map instead of only keys and would expect the
>>> library to have built-in API for this. Maybe for the future references it
>>> would be beneficial to add concrete code examples into motivation in the
>>> core.spec guide (
>>> https://clojure.org/about/spec#_map_specs_should_be_of_keysets_only)
>>> which would better illustrate the described benefits of the current lib
>>> behaviour?
>>>
>>
>>
>> This is all about evolution of specs over time. If you make something
>> "strict" then you are saying "this is not allowed". You thus can never
>> extend the key set in the future without causing breakage. Whereas if you
>> say what a key set must have and validate what it does have, you can also
>> grow the spec in the future. Rich expanded at length on this idea and this
>> particular case in https://www.youtube.com/watch?v=oyLBGkS5ICk .
>>
>> Alex
>>
>
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