Scala Note 16: Case Classes

Case classes are regular classes which export their constructor parameters and which provide a recursive decomposition mechanism via pattern matching.

abstract class Term
case class Var(name: String) extends Term
case class Fun(arg: String, body: Term) extends Term
case class App(f: Term, v: Term) extends Term

1. To facilitate the construction of case class instances, Scala does not require that the new primitive is used. One can simply use the class name as a function.
The constructor parameters of case classes are treated as public values and can be accessed directly.

val x = Var("x")
Console.println(x.name)

2. For every case class the Scala compiler generates equals method which implements structural equality and a toString method.

3. It makes only sense to define case classes if pattern matching is used to decompose data structures. 

object TermTest extends Application {
  def printTerm(term: Term) {
    term match {
      case Var(n) =>
        print(n)
      case Fun(x, b) =>
        print("^" + x + ".")
        printTerm(b)
      case App(f, v) =>
        Console.print("(")
        printTerm(f)
        print(" ")
        printTerm(v)
        print(")")
    }
  }}

Reference:

http://www.scala-lang.org/old/node/107.html