Generalize HasBuilder to enable modelling infallible constructors (for NewtypeWrapped in contrast to NewValidated)

[sideeffffect]

/cc @lgmyrek

[alexandru]

Hey, thanks for the PR.

Can you explain where having infallible constructors would help?

[sideeffffect]

For usage with NewtypeWrapped. That's just a wrapper, so there's no validation that could fail. Than you can coerce all typeclass implementations for A into NewtypeWrapped[A]. This is how we do it

  implicit class CoerceFOps[F[_], A](private val self: F[A]) extends AnyVal {
    def coerce[B](
      implicit
      extractor: HasExtractor.Aux[B, A],
      builder: HasBuilder.Aux[B, Nothing, A],
    ): F[B] = self.asInstanceOf[F[B]]
  }

[sideeffffect]

What do you think @alexandru , is this a sensible approach?

[sideeffffect]

Before we did it like this

  implicit class CoerceFOps[F[_], A](private val self: F[A]) extends AnyVal {
    def coerce[B <: NewtypeWrapped[A]#Type]: F[B] = self.asInstanceOf[F[B]]
  }

but we felt that it's cleaner to use the HasExtractor/HasBuilder type classes rather than <: NewtypeWrapped[A]#Type.

[alexandru]

I'm thinking yes, but let me think about it. I'm taking a look tonight, to play around with the code.

[sideeffffect]

Hello @alexandru , have you had a chance to consider this PR for merging? 😺