CS2340ObjectsandDesign-Scala.PDF

CS 2340 Objects and Design - Scala Case Classes Christopher Simpkins chris.simpkins@gatech.edu Chris Simpkins (Georgia Tech) CS 2340 Objects and Design - Scala Case Classes 1 / 23 Arithmetic Expressions abstract class Expr case class Var(name: String) extends Expr case class Number(num: Double) extends Expr case class UnOp(operator: String, arg: Expr) extends Expr case class BinOp(operator: String, left: Expr, right: Expr) extends Expr Each clase class extends either an abstract class or trait Bodies of classes are empty, typical of case classes Class parameters are implicitly defined as val fields (no val annotation required - save some typing) Chris Simpkins (Georgia Tech) CS 2340 Objects and Design - Scala Case Classes 2 / 23 Syntactic Conveniences 1/2 Factory Methods: scala val v = Var( x ) v: Var = Var(x) scala val op = BinOp(+, Number(1), v) op: BinOp = BinOp(+,Number(1.0),Var(x)) Implicit field definition (vals): scala v.name res0: String = x scala op.left res1: Expr = Number(1.0) Chris Simpkins (Georgia Tech) CS 2340 Objects and Design - Scala Case Classes 3 / 23 Syntactic Conveniences 2/2 “Naturally” defined toString and == in terms of equals: scala println(op) BinOp(+,Number(1.0),Var(x)) scala op.right == Var(x ) res3: Boolean = true copy method: scala op.copy(operator = -) res4: BinOp = BinOp(-,Number(1.0),Var(x)) Chris Simpkins (Georgia Tech) CS 2340 Objects and Design - Scala Case Classes 4 / 23 Simplifying Arithmetic Expressions Say we want to simplify arithmetic expressions. UnOp( -, UnOp(-, e)) = e // Double negation BinOp( +, e, Number(0)) = e // Adding zero BinOp( *, e, Number(1)) = e // Multiplying by one In other words,