Question

我对使用相同对象的方法访问对象的私有内部类有点困惑。这是我在Scala编程中的练习代码（第245-246页）：

import Element.elem

abstract class Element {
    def contents: Array[String]
    def height = contents.length
    def width = if(height == 0) 0 else contents(0).length

    def above(that: Element): Element = elem(this.contents ++ that.contents)

    def beside(that: Element): Element = {
    elem( for(
            (line1, line2) <- this.contents zip that.contents)
            yield line1 + line2 )
    }

    override def toString = contents mkString "\n"
 }


 object Element {

    private class ArrayElement (
            val contents: Array[String]
    ) extends Element

    private class LineElement (s: String) extends ArrayElement(Array(s)) {
            override def width = s.length
            override def height = 1
    }

    private class UniformElement (
            val ch: Character,
            override val width: Int,
            override val height: Int
    ) extends Element {
            private val line = ch.toString * width
            def contents = Array.fill(height)(line)
    }

    def elem(ss: Array[String]) = new ArrayElement(ss)
    def elem(s: String) = new LineElement(s)
    def elem(ch: Character, w: Int, h: Int) = new UniformElement(ch, w, h)

 }

代码与书中的代码相同，但编译器抱怨Element对象底部的三个def elem()方法。错误说：

私有类ArrayElement将其定义范围作为类型的一部分进行转义 pis.Code_c10s02_CompositionAndInheritance.Element.ArrayElement

但是，如果我从内部类中删除private修饰符，一切都会变好。这不应该是解决方案，本书的这一部分似乎主要是关于对象内的类进行私有化。这里我的错误是什么？

Answer 1

出于某种原因，它宁愿失败编译而不是推断一个不太具体但公开的类型。用返回类型声明elem方法。

def elem(ss: Array[String]): Element             = new ArrayElement(ss)
def elem(s: String): Element                     = new LineElement(s)
def elem(ch: Character, w: Int, h: Int): Element = new UniformElement(ch, w, h)

Scala对象具有内部类和方法的私有范围

1 个答案: