如何在子类中实现部分函数

Question

我正在尝试设计几个继承部分函数的类，但我似乎无法正确地获得语法。我的超类看起来像这样：

abstract class Controller {

    val react:PartialFunction[Event,Unit]

}

子类看起来像：

class BoardRendererController(val renderer:BoardRenderer, val board:Board) extends Controller {

    override val react {
        case PieceMovedEvent(piece, origin, destination) => println("Moving now")
    }
}

但是这个错误无法编译

[ERROR] /workspace/pacman/src/main/scala/net/ceilingfish/pacman/BoardRendererController.scala:14: error: '=' expected but '{' found.
[INFO]  override val react {
[INFO]                            ^
[ERROR] /workspace/pacman/src/main/scala/net/ceilingfish/pacman/BoardRendererController.scala:17: error: illegal start of simple expression
[INFO] }
[INFO] ^

我已尝试过大量的变体，有人知道正确的语法是什么吗？

Answer 1

除了abhin4v的简洁建议之外，您还必须在定义中提供类型注释，因此我建议您在基类中添加此类注释：

type PFEU = PartialFunction[Event, Unit]

然后你的子类看起来像这样：

class BoardRendererController(val renderer:BoardRenderer, val board:Board)
extends Controller
{
    override val react: PFEU = {
        case PieceMovedEvent(piece, origin, destination) => println("Moving now")
    }
}