CODEWITHSUNDEEP
scala
matanox
matanox

Reputation: 13746

Extending a scala class with less ceremony

I am probably doing something wrong. When I extend a class, I specify the mapping between the extendee's constructor and the extended class constructor:

class Base(one: String, two: String)
case class Extended(one: String, two: String, three: String) extends Base(one, two)

How can I instead suffice with something like any of the following, thus implying a "default" mapping?

class Base(one: String, two: String) 
case class Extended(one: String, two: String, three: String) extends Base

class Base(one: String, two: String) 
case class Extended(three: String) extends Base

I am probably missing the cleaner way of just adding a parameter without all that ceremony. Or should I be using a trait rather than subclassing, for such simple thing....

Upvotes: 3

Views: 146

Answers (1)

misberner
misberner

Reputation: 3688

All the parameters of a case class generated apply method have to be specified in the case class declaration, so your second proposal cannot work. The first one can be accomplished if Base is abstract, using abstract vals:

abstract class Base {
  // no initializers!
  val one : String
  val two : String

  def print { println("Base(%s, %s)" format (one, two)) }
}
// Note: constructor arguments of case classes are vals!
case class Extended(one: String, two: String, three: String) extends Base
...
Extended("foo", "bar", "baz").print // prints 'Base(foo, bar)'

However, the names need to match exactly.

Upvotes: 10

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