Question

所以，我必须并行类结构，Books和Makers。制作者根据某个文件或其他内容创建一本书。我们可以将基本Maker的定义简化为：

class Maker {
  type PF = (String, Book) => Book
  def apply(in: Source): Book = {
    mkMap(in, parseTop)
  }
  def mkMap(in: Source, top: PF) {
    var res = new Book
    in.getLines.foreach { ln => res = top(ln, res)
  }
  def parseTop(line: String, book: Book): Book = {
    // really makes a new Book object with changes based on the content of `line` and returns it
    book
  }
}

和Book看起来像这样（不是case class，因为我们希望能够继承它）

class Book(val title: String = "Untitled", val author: String = "No Author", val language: String = "English")
  def copy(title: String = this.title, author: String = this.author, language: String = this.language) = new Book(title, author, language)

现在，我想将其扩展为制作SpecialMaker SpecialBooks。特别书可以这样定义：

class SpecialBook(title: String = "Untitled", author: String = "No Author", language: String = "English", val specialness: Int = 9000) extends Book(title, author, language)
  def copy(title: String = this.title, author: String = this.author, language: String = this.language, specialness: Int = this.specialness) = new SpecialBook(title, author, language, specialness)

从SpecialBook制作Book时唯一的变化是parseTop函数会做一些额外的计算来制作特殊因素，让我们这样说：

class SpecialMaker {
   override def parseTop(line: String, book: SpecialBook): SpecialBook = {
     book.copy(specialness = book.specialness + 9000)
   }
}

显然，该代码不起作用，因为parseTop最终将BookBook分配给Book，以及其他问题。什么是在Scala中处理问题的最佳方法？隐含的转换？（可以与类型参数有关吗？）

如果有设计模式处理此问题，请告诉我它的名称。

什么是在scala中实现此目的的正确方法

1 个答案: