ch01 multi-currency money

Chapter01.scala

package fp_tdd

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

object Chapter01 extends Properties("Ch01") {
// ======== TODO ========
// $5 + 10 CHF = $10 if rate is 2:1
// Make "amount" private
// Dollar side effect
// Money rounding?
// ======== DONE ========
// 1. $5 * 2 = $10

// product code -------------------------------------------------------------------
  class Dollar(var amount: Int) {
    def times(multiplier: Int): Unit = amount = amount * multiplier
  }
// properties -------------------------------------------------------------------
  property("$0 * x = $0") = forAll { (x: Int) =>
    val zero: Dollar = new Dollar(0)
    zero.times(x)
    zero.amount == 0
  }
  property("$1 * x = $x") = forAll { (x: Int) =>
    val five: Dollar = new Dollar(1)
    five.times(x)
    five.amount == x
  }
  property("$a * b = $b * a") = forAll { (a: Int, b: Int) =>
    val d1: Dollar = new Dollar(a)
    d1.times(b)
    val d2: Dollar = new Dollar(b)
    d2.times(a)
    d1.amount == d2.amount
  }
  property("($a * b) * c = $a * (b * c)") = forAll { (a: Int, b: Int, c: Int) =>
    val d1: Dollar = new Dollar(a)
    d1.times(b)
    d1.times(c)
    val d2: Dollar = new Dollar(a)
    d2.times(b * c)
    d1.amount == d2.amount
  }
}