Track parent tag of properties #13

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1. cornerman

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   enhancement

   on Nov 17, 2017
2. raquo commented on Nov 17, 2017

   

   raquo

   on Nov 17, 2017

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   Looks like there's two distinct problems here:

   P1) Provide type of parent element to keys (attrs / props / etc.)
   P2) Restrict type of parent element for each key

   Regarding P1, see outwatch/outwatch#93 (comment) for a possible solution. The idea is that the key itself does not need the type, it's the := method that does, so maybe we can provide the type to it instead.

   Regarding P2 – Suppose we could indeed define the type of value as ApplesTo[ParentEl: dom.html.Button | dom.html.Input | dom.html.Option]. We could then restrict the types provided in P1 to a subtype of ParentEl, ensuring that we don't call value := x on elements that don't support value.

   However, the ParentEl type from P2 is by itself not very useful – e.g. we can't call .value on such a type, and it only works in Scala.js.

   So for things like currentTarget typing, we would need P1 but not P2.

   ---

   As an alternative to | we can have multiple value attrs: def value: AppliesTo[dom.html.Input], def value: AppliesTo[dom.html.Button], etc. but this has its own problems, both for performance (need to instantiate many more objects) and convenience (can't do if (attr == value) anymore).
3. raquo commented on Nov 17, 2017

   

   raquo

   on Nov 17, 2017

   Last edited by raquo

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   Hmm instead of defining value as ApplesTo[ParentEl: dom.html.Button | dom.html.Input | dom.html.Option] we could define somewhat like this:

   Note: I haven't tried to compile any of that. Not sure if it would work.

   trait ValueAttr
   
   trait AppliesTo[T, P] {
     type Parent = P
   }
   implicit object valueAppliesToInput AppliesTo[Value, dom.html.Input]
   implicit object valueAppliesToButton extends AppliesTo[Value, dom.html.Button]
   

   lazy val value: Attr[String, ValueAttr]
   

   And then:

   class Attr[V, T] {
     def :=[Parent](value: V)(implicit appliesTo: AppliesTo[T, Parent])
   }
   

   and similarly:

   class EventProp[T] {
     def :=[Parent](value: TargetedEvent[Parent] =>())(implicit appliesTo: AppliesTo[T, Parent])
   }
   

   👍React with 👍1Reacted by johannes karoff