Type Parameters and Generics

Generic Box Value

Store one value in a class with a type parameter.

generic-class A class can take a type parameter too. `Box[A]` stores one value while keeping the value's type known to the compiler.

Generic Box Value

points
GenericBoxValue.scala
Replay: real traced execution (multi-file project)
case class Box[A](value: A)

object Main {
  def main(args: Array[String]): Unit = {
    val points = 12
    val box = Box[Int](points)
    val doubled = box.value * 2

    println("value=" + box.value)
    println("doubled=" + doubled)
  }
}

case class Box[A](value: A)

object Main {
  def main(args: Array[String]): Unit = {
    val points = 5
    val box = Box[Int](points)
    val doubled = box.value * 2

    println("value=" + box.value)
    println("doubled=" + doubled)
  }
}

case class Box[A](value: A)

object Main {
  def main(args: Array[String]): Unit = {
    val points = 20
    val box = Box[Int](points)
    val doubled = box.value * 2

    println("value=" + box.value)
    println("doubled=" + doubled)
  }
}

  1. points ← 12, box ← Box(12), doubled ← 24

    3object Main {4  def main(args: Array[String]): Unit = {5    val points→ 12 = 12 //@points=5, 206    val box→ Box(12) = Box[Int](points12)7    val doubled→ 24 = boxBox(12).value * 289    println("value=" + box.value12)10    println("doubled=" + doubled24)11  }12}
    outputvalue=12
doubled=24

  1. points ← 5, box ← Box(5), doubled ← 10

    3object Main {4  def main(args: Array[String]): Unit = {5    val points→ 5 = 56    val box→ Box(5) = Box[Int](points5)7    val doubled→ 10 = boxBox(5).value * 289    println("value=" + box.value5)10    println("doubled=" + doubled10)11  }12}
    outputvalue=5
doubled=10

  1. points ← 20, box ← Box(20), doubled ← 40

    3object Main {4  def main(args: Array[String]): Unit = {5    val points→ 20 = 206    val box→ Box(20) = Box[Int](points20)7    val doubled→ 40 = boxBox(20).value * 289    println("value=" + box.value20)10    println("doubled=" + doubled40)11  }12}
    outputvalue=20
doubled=40