loans.scala

object Loan {
  trait Close[A] {
    def close(a: A): Unit
  }

  object Close {
    private def closeQ[A: Close](a: A): Boolean =
      try { implicitly[Close[A]].close(a); true }
      catch { case _: Exception => false }
    implicit def Tuple2Close[A: Close, B: Close] = new Close[(A, B)] {
      def close(t: (A, B)) { closeQ(t._1) && closeQ(t._2) }
    }
    implicit def Tuple3Close[A: Close, B: Close, C: Close] = new Close[(A, B, C)] {
      def close(t: (A, B, C)) = { closeQ(t._1) && closeQ(t._2) && closeQ(t._3) }
    }
  }

  type Connection = Unit
  type Session = Int
  type User = String

  implicit val ConnectionClose = new Close[Connection] { def close(c: Connection) {} }
  implicit val SessionClose = new Close[Session] { def close(c: Session) {} }
  implicit val UserClose = new Close[User] { def close(c: User) {} }

  def database: Connection = ()
  def session = 2
  def user = "Bob"

  def withA[A: Close, B](a: A)(f: A => B): B = f(a)

  withA((database, session, user)) {
    case (db, s, u) =>
      println("hi")
  }
}