case class overloading in Scala
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12-06-2021 - |
質問
I have a legacy message in my system, and I would like to be able to map it new version the message in my system.
Why can't I overload my case class?
case class Message(a:Int, b:Int)
case class NewMessage(a:Int, b:Int, c:Int) {
def this(msg : Message) = this(a = msg.a, b = msg.b, c = 0)
}
val msg = Message(1,2)
val converted = NewMessage(msg)
This code doesn't seem to compile. :(
解決
You must explicitly call constructor by using new
operator:
val converted = new NewMessage(msg)
It works because you are actually defining a second constructor in NewMessage
while ordinary:
NewMessage(1, 2, 3)
is translated to:
NewMessage.apply(1, 2, 3)
他のヒント
You're overloading the constructor, while what you want to do is overload the apply method. You can do this on the companion object:
case class NewMessage(a: Int, b: Int, c: Int)
object NewMessage {
def apply(msg: Message) = new NewMessage(a = msg.a, b = msg.b, c = 0)
}
val converted = NewMessage(msg)
所属していません StackOverflow