Is it correct to define all classes as cases in Scala just to have all their arguments made properties automatically?

Question

I'm beginning Scala. Am I correct understanding that I should define a class as a case class if I'd like it's arguments to be exposed as properties? Does not it introduce any side effects?

Answer 1

The boilerplate code generated for case classes carries a small but non-zero cost in bytecode. In addition to the copy method, there is hashCode, equals and toString as well as the companion object factory method.

More significant is the fact that it is inadvisable to derive classes from case classes. Deriving a case class from a case class really invites problems (and the compiler will yell at you). In particular, no overriding copy(...) method is generated by the compiler, so you can get some odd failure modes if you try to copy a case class derived from a case class.

If you keep your case classes at the leafs of any inheritance graphs, you'll be fine.

Answer 2

You will get properites for any parameters defined and they will be vals (i.e., finals)

case class User(name: String, group: String)
val user = User("jsmith", "admins")

// access both properties
println("name: %s group: %s".format(user.name, user.group))

You can get this behavior with regular (i.e., non-case classes) as well:

// creates two final public properties as well
class User(val name: String, val group: String)

// creates read/write public properties
class User(var name: String, var group: String)
val user = new User("jsmith", "admins")
user.group = "guests"

Case classes also bring a lot of other things as well such as a useful implementations of equality, hashcode and toString and a companion object with a factory method that eliminates the need to use new among other things.

As you can see, a case class is not required to achieve what you want but it gets you there quickly. As for side effects, defining a case class generates some bit of code behind the scenes to give you what was described in the previous paragraph. These are often useful and I tend not to worry about them but it is good to know about them.