type classes

tc.scala

    //============== the Type Class version

    trait Eq[A] { // the type trait
      def areTheSame(a: A, b: A): Boolean
    }

    case class Student(name: String) // better decoupling - extends nothing

    object EqImplementations { // the implementations for different classes
      implicit object EqStudent extends Eq[Student] {
        override def areTheSame(a: Student, b: Student) = a.name == b.name
      }
    }

    // all it says is that there must be an Eq implementation for A, somewhere in context
    def member[A: Eq](a: A, container: List[A]) =
      container.exists(implicitly[Eq[A]].areTheSame(_, a))

    import EqImplementations._ // bring it in context

    member(Student("John"), List(Student("John")))