filtered_case_class_comparison.scala

import shapeless.Generic
import shapeless.HList
import shapeless.ops.hlist.FilterNot
import java.util.UUID

// compare case classes but ignore UUID fields in the comparison

object ExampleApp {

  final case class Foo(
    a: String,
    b: Int,
    c: UUID,
    d: Int,
    e: UUID)

  def main(args: Array[String]): Unit = {
    val foo0 = Foo("hello", 1, UUID.randomUUID, 0, UUID.randomUUID)
    val foo1 = Foo("hello", 1, UUID.randomUUID, 0, UUID.randomUUID)

    println(foo0 == foo1) // false
    println(DataEq[Foo].eqv(foo0, foo1)) // true
  }

}

/** A type class used to determine the equality of the data between two
  * types
  */
sealed trait DataEq[A] {

  /** Returns true of the data for x and the data for y
    * are equivalent
    */
  def eqv(x: A, y: A): Boolean
}

object DataEq {

  def apply[A](implicit ev: DataEq[A]): DataEq[A] = ev

  def instance[A](f: (A, A) => Boolean): DataEq[A] = new DataEq[A] {
    def eqv(x: A, y: A): Boolean = f(x, y)
  }

  implicit def genProductDataEqIgnoreUUID[A, L0 <: HList, L1 <: HList](
    implicit
      gen: Generic.Aux[A, L0],
      fil: FilterNot.Aux[L0, UUID, L1]
  ): DataEq[A] = instance((x, y) =>
    fil(gen.to(x)) == fil(gen.to(y)))
}