从基本抽象类构造子类 [英] Constructing subclasses from base abstract class

问题描述

我想在抽象类中定义一个构造器，该构造器将创建具体的子类。

I want to define a constructor in an abstract class that will create concrete subclasses.

abstract class A {
  type Impl <: A
  def construct() : Impl = {
    val res = new Impl() //compile error: class type required but A.this.Impl found
    // do more initialization with res
  }
}

class B extends A {type Impl = B}
class C extends A {type Impl = C}
//...
val b = new B
b.construct() // this should create a new instance of B

这是怎么了？这甚至有可能实现吗？
编辑：澄清：我想对构造方法进行抽象。我不想从子类或伴随对象中分别调用 new B 和 new C 。

What is wrong here? Is this even possible to implement? Clarification: I want to abstract over the construct method. I do not want to call separately new B and new C from either subclasses or companion objects.

推荐答案

如果要创建新实例，则需要显式调用构造函数。

You need to explicitly invoke a constructor if you want create a new instance.

abstract class A {

  def newInstance(): this.type;

  def construct() : this.type = {
    val res = newInstance()
  }
}

class B extends A {
  def newInstance() = new B()
}

标量擦除在运行时键入Impl，因此无法了解创建类时Impl的含义。

Scala erases type at runtime so there is no way to know what Impl meant when the class was created.

这篇关于从基本抽象类构造子类的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！