What code is generated for an equals/hashCode method of a case class?

Question

I have some Java code which I'm translating to Scala.

The code consists of some immutable classes which would fit the purpose of a case class in Scala.

But I don't want to introduce bugs, therefore I want to be sure that the code being generated for equals and hashCode is/behaves equivalent to the current implementation.

I already looked in "Programming in Scala" but it only says

Third, the compiler adds “natural” implementations of methods toString, hashCode, and equals to your class.

Answer 1

Scala has a compiler option -Xprint:typer, which you can use to get the "post-typing source code that it uses internally".

scala -Xprint:typer -e 'case class Foo(a: String, b: Int)' 

Here you see something like:

override def hashCode(): Int = ScalaRunTime.this._hashCode(Foo.this); override def toString(): String = ScalaRunTime.this._toString(Foo.this); override def equals(x$1: Any): Boolean = Foo.this.eq(x$1).||(x$1 match {   case (a: String,b: Int)this.Foo((a$1 @ _), (b$1 @ _)) if a$1.==(a).&&(b$1.==(b)) => x$1.asInstanceOf[this.Foo].canEqual(Foo.this)   case _ => false }); 

But, this doesn't tell you how hashCode is generated. Here's the source for that:

def _hashCode(x: Product): Int = {   var code = x.productPrefix.hashCode()   val arr =  x.productArity   var i = 0   while (i < arr) {     val elem = x.productElement(i)     code = code * 41 + (if (elem == null) 0 else elem.hashCode())     i += 1   }   code } 

And, in this example, the first case of the equals pattern matching would just be:

case that: Foo => this.a == that.a && this.b == that.b