生成的代码工件

case 修饰符使 Scala 编译器自动为类生成通用样板代码。手动实现此代码非常繁琐且是错误的来源。以下案例类定义：

case class Person(name: String, age: Int)

…将自动生成以下代码：

class Person(val name: String, val age: Int)
  extends Product with Serializable
{
  def copy(name: String = this.name, age: Int = this.age): Person =
    new Person(name, age)

  def productArity: Int = 2

  def productElement(i: Int): Any = i match {
    case 0 => name
    case 1 => age
    case _ => throw new IndexOutOfBoundsException(i.toString)
  }

  def productIterator: Iterator[Any] =
    scala.runtime.ScalaRunTime.typedProductIterator(this)

  def productPrefix: String = "Person"

  def canEqual(obj: Any): Boolean = obj.isInstanceOf[Person]

  override def hashCode(): Int = scala.runtime.ScalaRunTime._hashCode(this)

  override def equals(obj: Any): Boolean = this.eq(obj) || obj match {
    case that: Person => this.name == that.name && this.age == that.age
    case _ => false
  }

  override def toString: String =
    scala.runtime.ScalaRunTime._toString(this)
}

case 修饰符还会生成一个伴随对象：

object Person extends AbstractFunction2[String, Int, Person] with Serializable {
  def apply(name: String, age: Int): Person = new Person(name, age)

  def unapply(p: Person): Option[(String, Int)] =
    if(p == null) None else Some((p.name, p.age))
}

当应用于 object 时，case 修饰符具有相似（尽管不那么显着）的效果。这里的主要收益是 toString 实现和跨进程一致的 hashCode 值。请注意，case 对象（正确）使用引用相等：

object Foo extends Product with Serializable {
  def productArity: Int = 0

  def productIterator: Iterator[Any] =
    scala.runtime.ScalaRunTime.typedProductIterator(this)

  def productElement(i: Int): Any =
    throw new IndexOutOfBoundsException(i.toString)

  def productPrefix: String = "Foo"

  def canEqual(obj: Any): Boolean = obj.isInstanceOf[this.type]

  override def hashCode(): Int = 70822 // "Foo".hashCode()

  override def toString: String = "Foo"
}

仍然可以手动实现 case 修饰符在类本身及其伴随对象中提供的方法。