Scala中此的类型 [英] Type of this in Scala

问题描述

是否有一种方法可以使方法始终返回调用它的同一类的类型?

Is there a way to make a method to always return the type of the same class that called it ?

让我解释一下:

class Shape {
  var mName: String = null
  def named(name: String): Shape = {
    mName = name
    this
  }
}

class Rectangle extends Shape {
  override def named(name: String): Rectangle = {
    super.named(name)
    this
  }
}

这有效，但是有没有一种方法可以不必在所有子类中覆盖named函数呢?我正在寻找类似的东西(不起作用):

This works, but is there a way to do this without having to override the named function in all of my subclasses? I'm looking for something like this (which does not work):

class Shape {
  var mName: String = null
  def named(name: String): classOf[this] = { // Does not work but would be great
    mName = name
    this
  }
}

class Rectangle extends Shape {
}

有什么主意吗?还是不可能?

Any idea ? Or is it not possible ?

推荐答案

您需要使用this.type而不是classOf[this].

class Shape {
  var mName: String = null
  def named(name: String): this.type = {
    mName = name
    this
  }
}

class Rectangle extends Shape {
}

现在要演示它的工作原理(在Scala 2.8中)

Now to demonstrate that it works (in Scala 2.8)

scala> new Rectangle().named("foo")
res0: Rectangle = Rectangle@33f979cb

scala> res0.mName
res1: String = foo

---

this.type是编译类型的名称，而classOf是在运行时被调用以获取java.lang.Class对象的运算符.您永远无法使用classOf[this]，因为该参数必须是类型名称.尝试获取java.lang.Class对象时，您的两个选择是调用classOf[TypeName]或this.getClass().

---

this.type is a compile-type type name, while classOf is an operator that gets called at runtime to obtain a java.lang.Class object. You can't use classOf[this] ever, because the parameter needs to be a type name. Your two options when trying to obtain a java.lang.Class object are to call classOf[TypeName] or this.getClass().

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