AboutEnumerations.scala

package org.functionalkoans.forscala

import support.KoanSuite
import org.scalatest.matchers.ShouldMatchers


class AboutEnumerations extends KoanSuite with ShouldMatchers {

// To create an enumeration, create an object that extends the abstract class Enumeration,
//          and set a val variable to the method Value.  This is a trick to give values to each val."
  koan("Value assigns a numerical value to fields") {

    object Planets extends Enumeration {
      val Mercury = Value
      val Venus = Value
      val Earth = Value
      val Mars = Value
      val Jupiter = Value
      val Saturn = Value
      val Uranus = Value
      val Neptune = Value
      val Pluto = Value
    }

    Planets.Mercury.id should be(0)
    Planets.Venus.id should be(1)

    Planets.Mercury.toString should be("Mercury") //How does it get the name? by Reflection.
    Planets.Venus.toString should be("Venus")

    (Planets.Earth == Planets.Earth) should be(true)
    (Planets.Neptune == Planets.Jupiter) should be(false)
  }

// You can create an enumeration with your own index and your own Strings, in this koan,
// we will start with an index of one and use Greek names instead of Roman
  koan("Enumerations can set their own index and name") {
    object GreekPlanets extends Enumeration {

      val Mercury = Value(1, "Hermes")
      val Venus = Value(2, "Aphrodite")
      //Fun Fact: Tellus is Roman for (Mother) Earth
      val Earth = Value(3, "Gaia")
      val Mars = Value(4, "Ares")
      val Jupiter = Value(5, "Zeus")
      val Saturn = Value(6, "Cronus")
      val Uranus = Value(7, "Ouranus")
      val Neptune = Value(8, "Poseidon")
      val Pluto = Value(9, "Hades")
    }

    GreekPlanets.Mercury.id should be(1)
    GreekPlanets.Venus.id should be(2)

    GreekPlanets.Mercury.toString should be("Hermes")
    GreekPlanets.Venus.toString should be("Aphrodite")

    (GreekPlanets.Earth == GreekPlanets.Earth) should be(true)
    (GreekPlanets.Neptune == GreekPlanets.Jupiter) should be(false)
  }

// Enumerations can be declared in one line if you are merely setting variables to Value
  koan("Enumeration declarations can be done on one line") {
    object Planets extends Enumeration {
      val Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto = Value
    }

    Planets.Mercury.id should be(0)
    Planets.Venus.id should be(1)

    Planets.Mercury.toString should be("Mercury") 
    Planets.Venus.toString should be("Venus")

    (Planets.Earth == Planets.Earth) should be(true)
    (Planets.Neptune == Planets.Jupiter) should be(false)
  }


  koan("Enumerations can be declared with a string value only") {
    object GreekPlanets extends Enumeration {

      val Mercury = Value("Hermes")
      val Venus = Value("Aphrodite")
      val Earth = Value("Gaia")
      val Mars = Value("Ares")
      val Jupiter = Value("Zeus")
      val Saturn = Value("Cronus")
      val Uranus = Value("Ouranus")
      val Neptune = Value("Poseidon")
      val Pluto = Value("Hades")
    }

    GreekPlanets.Mercury.id should be(0)
    GreekPlanets.Venus.id should be(1)

    GreekPlanets.Mercury.toString should be("Hermes")
    GreekPlanets.Venus.toString should be("Aphrodite")

    (GreekPlanets.Earth == GreekPlanets.Earth) should be(true)
    (GreekPlanets.Neptune == GreekPlanets.Jupiter) should be(false)
  }

  koan("You can extend the Enumeration by extending the Val class.") {

    object Planets extends Enumeration {

      val G = 6.67300E-11

      class PlanetValue(val i: Int, val name: String, val mass: Double, val radius: Double)
              extends Val(i: Int, name: String) {

        def surfaceGravity = G * mass / (radius * radius)

        def surfaceWeight(otherMass: Double) = otherMass * surfaceGravity

        def compare(that: PlanetValue) = this.i - that.i
      }

      val Mercury = new PlanetValue(0, "Mercury", 3.303e+23, 2.4397e6)
      val Venus = new PlanetValue(1, "Venus", 4.869e+24, 6.0518e6)
      val Earth = new PlanetValue(2, "Earth", 5.976e+24, 6.37814e6)
      val Mars = new PlanetValue(3, "Mars", 6.421e+23, 3.3972e6)
      val Jupiter = new PlanetValue(4, "Jupiter", 1.9e+27, 7.1492e7)
      val Saturn = new PlanetValue(5, "Saturn", 5.688e+26, 6.0268e7)
      val Uranus = new PlanetValue(6, "Uranus", 8.686e+25, 2.5559e7)
      val Neptune = new PlanetValue(7, "Neptune", 1.024e+26, 2.4746e7)
      val Pluto = new PlanetValue(8, "Pluto", 1.27e+22, 1.137e6)

    }

    Planets.Earth.mass should be(5.976e+24)
    Planets.Earth.radius should be(6.37814e6)
  }
}