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12 Packages, Imports, and Exports

Sample run of chapter's interpreter examples

• 12.1 Putting code in packages
• 12.2 Concise access to related code
• 12.3 Imports
• 12.4 Implicit imports
• 12.5 Access modifiers
• 12.6 Top-level definitions
• 12.7 Exports
• 12.8 Conclusion

12.1 Putting code in packages

// In file packages-and-imports/ex1/Ex1.scala

  package bobsrockets.navigation
  class Navigator


  package bobsrockets.navigation:
    class Navigator


  package bobsrockets:
    package navigation:

      // In package bobsrockets.navigation
      class Navigator

      package launch:

        // In package bobsrockets.navigation.launch
        class Booster


// In file packages-and-imports/ex4/Ex4.scala

  package bobsrockets:
    package navigation:

      class Navigator:
        // No need to say bobsrockets.navigation.StarMap
        val map = new StarMap

      class StarMap

    class Ship:
      // No need to say bobsrockets.navigation.Navigator
      val nav = new navigation.Navigator

    package fleets:

      class Fleet:
        // No need to say bobsrockets.Ship
        def addShip = new Ship


  package bobsrockets:
    class Ship

  package bobsrockets.fleets:
    class Fleet:
      // Doesn't compile! Ship is not in scope.
      def addShip = new Ship


// In file packages-and-imports/launch.scala

  // In file launch.scala
  package launch:
    class Booster3

  // In file bobsrockets.scala
  package bobsrockets:

    package launch:
      class Booster2

    package navigation:
      package launch:
        class Booster1

      class MissionControl:
        val booster1 = new launch.Booster1
        val booster2 = new bobsrockets.launch.Booster2
        val booster3 = new _root_.launch.Booster3


  

12.2 Concise access to related code

  package bobsrockets
  package fleets
  class Fleet:
    // No need to say bobsrockets.Ship
    def addShip = new Ship


  

12.3 Imports

// In file packages-and-imports/Fruits.scala

  package bobsdelights

  abstract class Fruit(
    val name: String,
    val color: String
  )

  object Fruits:
    object Apple extends Fruit("apple", "red")
    object Orange extends Fruit("orange", "orange")
    object Pear extends Fruit("pear", "yellowish")
    val menu = List(Apple, Orange, Pear)


// In file packages-and-imports/Ex5.scala

  // easy access to Fruit
  import bobsdelights.Fruit

  // easy access to all members of bobsdelights
  import bobsdelights.*

  // easy access to all members of Fruits
  import bobsdelights.Fruits.*


// In file packages-and-imports/Ex5.scala

  def showFruit(fruit: Fruit) =
    import fruit.*
    s"{name}s are color"


// In file packages-and-imports/Ex6.scala

  import java.util.regex

  class AStarB:
    // Accesses java.util.regex.Pattern
    val pat = regex.Pattern.compile("a*b")


// In file packages-and-imports/Ex7.scala

  import Laptops.*
  import Fruits.{Apple as _, *}


  

12.4 Implicit imports

  import java.lang.* // everything in the java.lang package
  import scala.*     // everything in the scala package
  import Predef.*    // everything in the Predef object


  

12.5 Access modifiers

// In file packages-and-imports/Ex8.scala.err

  class Outer:

    class Inner:
      private def f = "f"
      class InnerMost:
        f // OK

    (new Inner).f // error: f is not accessible


// In file packages-and-imports/Ex9.scala.err

  package p:

    class Super:
      protected def f = "f"

    class Sub extends Super:
      f

    class Other:
      (new Super).f  // error: f is not accessible


// In file packages-and-imports/ex10/Ex10.scala

 package bobsrockets

 package navigation:
   private[bobsrockets] class Navigator:
     protected[navigation] def useStarChart() = {}
     class LegOfJourney:
       private[Navigator] val distance = 100

 package launch:
   import navigation.*
   object Vehicle:
     private[launch] val guide = new Navigator


// In file packages-and-imports/Rocket.scala

  class Rocket:
    import Rocket.fuel
    private def canGoHomeAgain = fuel > 20

  object Rocket:
    private def fuel = 10
    def chooseStrategy(rocket: Rocket) =
      if rocket.canGoHomeAgain then
        goHome()
      else
        pickAStar()

    def goHome() = {}
    def pickAStar() = {}


  

12.6 Top-level definitions

// In file packages-and-imports/package.scala

  // In file ShowFruit.scala
  package bobsdelights

  def showFruit(fruit: Fruit) =
    import fruit.*
    s"{name}s are color"

  // In file PrintMenu.scala
  package printmenu

  import bobsdelights.Fruits
  import bobsdelights.showFruit

  object PrintMenu:
    def main(args: Array[String]) =
      println(
        for fruit <- Fruits.menu yield
          showFruit(fruit)
      )


  

12.7 Exports

  case class PosInt(value: Int):
    require(value > 0)


  val x = PosInt(88)
  x.value + 1 // 89


  case class PosInt(value: Int):
    require(value > 0)
    def +(x: Int): Int = value + x


  val x = PosInt(77)
  x + 1 // 78


  case class PosInt(value: Int):
    require(value > 0)
    export value.*


  val x = PosInt(99)
  x + 1 // 100
  x - 1 // 98
  x / 3 // 33


  final def +(x: Int): Int = value + x


  val x = PosInt(24)
  x << 1  // 48 (shift left)
  x >> 1  // 12 (shift right)
  x >>> 1 // 12 (unsigned shift right)


  case class PosInt(value: Int):
    require(value > 0)
    export value.{<< as shl, >> as shr, >>> as ushr, *}


  val x = PosInt(24)
  x shl 1  // 48
  x shr 1  // 12
  x ushr 1 // 12


  case class PosInt(value: Int):
    require(value > 0)
    export value.{<< as shl, >> as shr, >>> as _, *}


  scala> val x = PosInt(39)
  val x: PosInt = PosInt(39)

  scala> x shr 1
  val res0: Int = 19

  scala> x >>> 1
  1 |x >>> 1
    |^^^^^
    |value >>> is not a member of PosInt


  

12.8 Conclusion