hashCode in case classes in Scala

Question

I've read that Scala'a case class construct automatically generates a fitting equals and hashCode implementation. What does exactly the generated code look like?

Answer 1

As my professor used to say, only the code tells the truth! So just take a look at the code that is generated for:

case class A(i: Int, s: String)

We can instruct the Scala compiler to show us the generated code after the different phases, here after the typechecker:

% scalac -Xprint:typer test.scala
[[syntax trees at end of typer]]// Scala source: test.scala
package <empty> {
  @serializable case class A extends java.lang.Object with ScalaObject with Product {
    ..
    override def hashCode(): Int = ScalaRunTime.this._hashCode(A.this);
    ...
    override def equals(x$1: Any): Boolean = A.this.eq(x$1).||(x$1 match {
      case (i: Int,s: String)A((i$1 @ _), (s$1 @ _)) if i$1.==(i).&&(s$1.==(s)) => x$1.asInstanceOf[A].canEqual(A.this)
      case _ => false
    });


    override def canEqual(x$1: Any): Boolean = x$1.$isInstanceOf[A]()
  };
}

So you can see that the calculation of the hash code is delegated to ScalaRunTime._hashCode and the equality depends on the equality of the case class' members.