Macro to turn multiple implicits of type M[T1 <: T] into single M[T] when T is sealed.
Requirement is, that all methods of M[T] need to have exactly one discriminator parameter of type T.
trait M[T] {
def do(t: T): String
def doI(i: Int, t: T):String
def doS(s: String)(t: T):String
} Macro would generate for you pattern matches using type of that discriminator parameter, and delegate execution to one of available in scope implicits M[T1 <: T].
sealed trait Product {
def name: String
def unitPrice: BigDecimal
}
case class Phone(name: String, unitPrice: BigDecimal) extends Product
case class Accessory(name: String, unitPrice: BigDecimal) extends Product
trait Pricer[T] {
def calculatePrice(t: T, quantity: Int): BigDecimal
}
object StandardPrices {
implicit val phonePricer = new Pricer[Phone] {
def calculatePrice(p: Phone, quantity: Int): BigDecimal = p.unitPrice * quantity
}
implicit val accessoryPricer = new Pricer[Accessory] {
def calculatePrice(p: Accessory, quantity: Int): BigDecimal = p.unitPrice * quantity
}
}
object SecondAccessoryFor1Cent {
implicit val accessoryPricer = new Pricer[Accessory] {
def calculatePrice(p: Accessory, quantity: Int): BigDecimal = {
val normalPriced = Math.ceil(quantity / 2.0).toInt
val for1centPriced = quantity - normalPriced
p.unitPrice * normalPriced + BigDecimal(0.01) * for1centPriced
}
}
}
object Main extends App {
val standardPricer: Pricer[Product] = {
import explicitImplicits._
import StandardPrices.phonePricer
import StandardPrices.accessoryPricer
deriveFromImplicits[Product, Pricer]
}
val promotionalPricer: Pricer[Product] = {
import explicitImplicits._
import StandardPrices.phonePricer
import SecondAccessoryFor1Cent.accessoryPricer
deriveFromImplicits[Product, Pricer]
}
val shoppingCart: Map[Product, Int] = Map(
Phone("Nexus 5", 100.0) -> 1,
Accessory("Qi charger", 30) -> 3
)
val standardCartValues = shoppingCart.map(standardPricer.calculatePrice _ tupled)
// standardCartValues: collection.immutable.Iterable[BigDecimal] = List(100.0, 90)
val promotionalCartValues = shoppingCart.map(promotionalPricer.calculatePrice _ tupled)
// promotionalCartValues: collection.immutable.Iterable[BigDecimal] = List(100.0, 60.01)
}resolvers += Resolver.bintrayRepo("lustefaniak", "maven")
libraryDependencies += "com.lustefaniak.explicitimplicits" %% "explicit-implicits" % "0.1.1"Or use demo project