ch02 degenerate objects

Chapter02.scala

package fp_tdd

import org.scalacheck.Prop.forAll
import org.scalacheck.Properties

object Chapter02 extends Properties("Ch02") {
  // ======== TODO ========
  // $5 + 10 CHF = $10 if rate is 2:1
  // Make "amount" private
  // Money rounding?
  // ======== DONE ========
  // 1. $5 * 2 = $10
  // 2. Dollar side effect
  // 2. times -> `*`

// product code -------------------------------------------------------------------
  case class Dollar(amount: Int) {
    def *(multiplier: Int): Dollar = Dollar(amount * multiplier)
  }

// properties -------------------------------------------------------------------
  property("$0 * x = $0") = forAll { (x: Int) =>
    Dollar(0) * x == Dollar(0)
  }
  property("$1 * x = $x") = forAll { (x: Int) =>
    Dollar(1) * x == Dollar(x)
  }
  property("$a * b = $b * a") = forAll { (a: Int, b: Int) =>
    Dollar(a) * b == Dollar(b) * a
  }
  property("($a * b) * c = $a * (b * c)") = forAll { (a: Int, b: Int, c: Int) =>
    (Dollar(a) * b) * c == Dollar(a) * (b * c)
  }
}