Scala Case Classes
Examples
Case Class Equality
One feature provided for free by case classes is an auto-generated equals method that checks the value equality of all individual member fields instead of just checking the reference equality of the objects.
With ordinary classes:
class Foo(val i: Int)
val a = new Foo(3)
val b = new Foo(3)
println(a == b)// "false" because they are different objectsWith case classes:
case class Foo(i: Int)
val a = Foo(3)
val b = Foo(3)
println(a == b)// "true" because their members have the same valueGenerated Code Artifacts
The case modifier causes the Scala compiler to automatically generate common boilerplate code for the class. Implementing this code manually is tedious and a source of errors. The following case class definition:
case class Person(name: String, age: Int)... will have the following code automatically generated:
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)
}
The case modifier also generates a companion object:
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))
}