Compose field validation

[MateuszKubuszok]

Given:

case class A(...)
case class A2(...)
case class B(a: A, a2: A2)

val av: Validator[A] = ...
val bv: Validator[B] = ...

right now, we are only able to use av inside bv if we make av implicit and use it during derivation. If we wanted to enhance some existing av, e.g. created with comap, we would have to do something like:

implicit val av: Validator[A] = ...

implicit val a2v: Validator[A2] = Validator[A2] // empty validator just for the sake of derivation

val bv: Validator[B] = ...

bv.composeDerived

which can generate some boilerplate at a times (the bigger B gets the more we will notice that). Given that there is already existing syntax for validating fields it would be intuitive to provide something like:

bv.rule(_.a, av)

[krzemin]

I guess compose or composeSuper may help you in such case.

Look also at this example: #10 (comment)

[krzemin]

Closing due to inactivity.