分数オブジェクトRational メソッド> + - * / 約分 ができる

FunctionalObjects_6.scala

package PSSE.code

//class Rational(n: Int, d: Int) {
//  require(d != 0) // falseならば､IllegalArgumentExceptionを投げる
//  override def toString = n + "/" + d
//}

// thatはaddメソッド呼びだしのレシーバーではないので､that.nとかthat.dとすることはできない※
// thatの分子や分母にアクセスするには､それらをフィールドにする必要がある
//class Rational(n: Int, d: Int) { // This won't compile
//  require(d != 0)
//  override def toString = n +"/"+ d
//  def add(that: Rational): Rational =
//    new Rational(n * that.d + that.n * d, d * that.d)
//}

// < lessThanメソッド の追加 >
//class Rational(n: Int, d: Int) {
//  require(d != 0)
//  val numer: Int = n
//  val denom: Int = d
//  
//  override def toString = numer +"/"+ denom
//  
//  // 他の分数との足し算を行う
//  def add(that: Rational): Rational =
//    new Rational(
//      numer * that.denom + that.numer * denom,
//      denom * that.denom
//    )
//  // 他の分数よりも小さいかどうか
//  def lessThan(that: Rational) =
//    this.numer * that.denom < that.numer * this.denom
//  
//  // 大きい方の分数を返す
//  def max(that: Rational) =
//    if (this.lessThan(that)) that else this
//}

// < 補助コンストラクターを追加したRationalクラス
// 補助コンストラクターは､先頭をdef this(..）とする｡ >
//class Rational(n: Int, d: Int) {
//
//  require(d != 0)
//
//  val numer: Int = n
//  val denom: Int = d
//
//  def this(n: Int) = this(n, 1) // auxiliary constructor
//
//  override def toString = numer +"/"+ denom
//
//  def add(that: Rational): Rational =
//    new Rational(
//      numer * that.denom + that.numer * denom,
//      denom * that.denom
//    )
//}

// < gcdメソッドの追加 >
//class Rational(n: Int, d: Int) {
//
//  require(d != 0)
//  private val g = gcd(n.abs, d.abs)
//
//  val numer: Int = n / g
//  val denom: Int = d / g
//
//  def this(n: Int) = this(n, 1) // auxiliary constructor
//
//  override def toString = numer +"/"+ denom
//
//  def add(that: Rational): Rational =
//    new Rational(
//      numer * that.denom + that.numer * denom,
//      denom * that.denom
//    )
//  // 約分をする
//  private def gcd(a: Int, b: Int): Int =
//    if (b == 0) a else gcd(b, a % b)
//}

// <add を + に変更。* を追加。>
//class Rational(n: Int, d: Int) {
//
//  require(d != 0)
//  private val g = gcd(n.abs, d.abs)
//
//  val numer: Int = n / g
//  val denom: Int = d / g
//
//  def this(n: Int) = this(n, 1) // auxiliary constructor
//
//  override def toString = numer +"/"+ denom
//
//  def + (that: Rational): Rational =
//    new Rational(
//      numer * that.denom + that.numer * denom,
//      denom * that.denom
//    )
//  def * (that: Rational): Rational =
//    new Rational(numer * that.numer, denom * that.denom)
//  // 約分をする
//  private def gcd(a: Int, b: Int): Int =
//    if (b == 0) a else gcd(b, a % b)
//}

// < 多重定義(overload) > 
class Rational(n: Int, d: Int) {

  require(d != 0)

  private val g = gcd(n.abs, d.abs)
  val numer = n / g
  val denom = d / g

  def this(n: Int) = this(n, 1)

  def + (that: Rational): Rational =
    new Rational(
      numer * that.denom + that.numer * denom,
      denom * that.denom
    )

  def + (i: Int): Rational =
    new Rational(numer + i * denom, denom)

  def - (that: Rational): Rational =
    new Rational(
      numer * that.denom - that.numer * denom,
      denom * that.denom
    )

  def - (i: Int): Rational =
    new Rational(numer - i * denom, denom)

  def * (that: Rational): Rational =
    new Rational(numer * that.numer, denom * that.denom)

  def * (i: Int): Rational =
    new Rational(numer * i, denom)

  def / (that: Rational): Rational =
    new Rational(numer * that.denom, denom * that.numer)

  def / (i: Int): Rational =
    new Rational(numer, denom * i)

  override def toString = numer +"/"+ denom

  private def gcd(a: Int, b: Int): Int =
    if (b == 0) a else gcd(b, a % b)
}

object FunctionalObjects_6 extends App{
  
  val oneHalf = new Rational(1, 2)
  val twoThirds = new Rational(2, 3)
  
  println(oneHalf + twoThirds) // 7/6
  println(oneHalf + oneHalf * twoThirds) // 5/6
  println(oneHalf + (oneHalf * twoThirds)) // 5/6
  
  println("oneHalf.numer = " + oneHalf.numer) // oneHalf.numer = 1
  println("oneHalf.denom = " + oneHalf.denom) // oneHalf.denom = 2

  //  println(oneHalf lessThan twoThirds)
  //  println(oneHalf max twoThirds)

  println(new Rational(3)) // 3/1

  println(new Rational(66, 42)) // 11/7
  
  println(new Rational(2, 1) + 2) // 4/1
  println(new Rational(2, 3) * 2) // 4/3
  
  // (Int * Rational)では引数が合わないのでエラーとなる。
  // 自動的に整数を分数に変換する暗黙の型変換を定義し解決。
  implicit def intToRational(x: Int) = new Rational(x)
  println(2 * new Rational(2,3))

  
}