What's behind Scala case classes?

Question

I'm quite new to Scala but I have already used case classes. I understood what are main differences between a regular class and a case class as summarized here .

I do not even think to get rid of case classes, but I would like to know what's the code needed to transform for example, this:

class Tweet(val user: String, val text: String) {
  override def toString: String =
    "User: " + user + "\n" +
    "Text: " + text + "]"
}

into a full case "compatible" class. I mean, I would like to code the same "behavior" of a case class but without using case keyword. Is this possible or does the compiler do something that I cannot get through code (excluding optimizations)?

Once again to make clear what I'm asking, I will always use case keyword when I need a case class, but once in life time, I would like to know what the Scala compiler (in generic sense) does for me, expressed in code terms.

edit: An additional doubt: will the compiler mark somehow differently my hand coded class from an standard case class so that I can observe a different behavior in execution?

Answer 1

You can have a look at chapter 5.3.2 "Case Classes" in the scala spec.

If I summarize correctly, the following is auto-generated:

• accessors are generated for the class elements
• an extractor object with apply/unapply is automatically generated
• a method copy is automatically added
• methods equals, hashCode, toString are overriden

You could compare the scala source and the generated java bytecode to be sure.