Defining implicit view-bounds on Scala traits

Question

I\'m doing an exercise to implement a functional binary-search-tree in Scala, following a similar pattern that I\'ve seen used in Haskell. I have a structure that looks somethin

Answer 1

@ben-james's answer is great, I would like improve it a bit to avoid redundant vals in classes.

The idea is to define implicit constructor parameter name the same as it is defined in trait that holds implicit value.

The idea is to avoid this line:

val evidence = ev

Here is a complete example (gist)

trait PrettyPrinted[A] extends (A => String)

object PrettyPrinted {
  def apply[A](f: A => String): PrettyPrinted[A] = f(_)
}

trait Printable[A] {
  implicit def printer: PrettyPrinted[A]
}

// implicit parameter name is important
case class Person(name: String, age: Int)
                 (implicit val printer: PrettyPrinted[Person])
  extends Printable[Person]

object Person {
  implicit val printer: PrettyPrinted[Person] =
    PrettyPrinted { p =>
      s"Person[name = ${p.name}, age = ${p.age}]"
    }
}

// works also with regular classes
class Car(val name: String)
         (implicit val printer: PrettyPrinted[Car])
  extends Printable[Car]

object Car {
  implicit val printer: PrettyPrinted[Car] =
    PrettyPrinted { c =>
      s"Car[name = ${c.name}]"
    }
}