CODEWITHSUNDEEP
scalacase-class
gav.newalkar
gav.newalkar

Reputation: 302

How can I copy a case class with its trait?

I have the following:

scala> trait Tail
scala> case class Cat(name: String)
scala> val aa = new Cat(name = "bob")
val aa: Cat with Tail = Cat(ben)
scala> val bb = aa.copy(name = "ted")
val bb: Cat = Cat(ted)

Why is it that bb didn't inherited the Tail trait?

How can I copy aa and still preserve the trait?

Upvotes: 2

Views: 505

Answers (1)

Alexey Romanov
Alexey Romanov

Reputation: 170735

val aa: Cat with Tail = Cat(ben)

Given the line above, this shouldn't happen. I assume you instead had

scala> val aa = new Cat(name = "ben") with Tail

In this case, it inherits copy from Cat, and the definition is given in Scala Language Specification. Following it, you can see that aa.copy("ted") just calls the constructor and returns new Cat("ted").

If you want to return Cat with Tail, you could implement it manually:

val aa = new Cat(name = "ben") with Tail {
  override def copy(name: String): Cat with Tail = new Cat(name) with Tail
}

or declare a separate class, but there's no built-in support. If you made the subclass a case class, it would get its own copy method, but a case class can't extend a case class; so in that case, Cat shouldn't be a case class.

Upvotes: 1

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