Scala的特征和方法参数

Question

在Scala中这叫什么？ 这被认为是多态性吗？

说我有一个像这样的旧方法：

def close(pair: TradingPair, currentDate: LocalDate, startTime: Long): Unit = {
    ...

    if (rowsWritten > 0) ZipWriter.compressAndDeleteOriginals(file)
    else file.delete()
  }

但我希望是这样的：

def close(pair: TradingPair, currentDate: LocalDate, startTime: Long, writer: CompressionWriter): Unit = {
     ...

    if (rowsWritten > 0) writer.compressAndDeleteOriginals(file)
  }

因为我期望更多类型的压缩编写器。 是执行此操作的好方法：

trait CompressionWriter {...}
object ZipWriter extends CompressionWriter {...}
object GZipWriter extends CompressionWriter {...}

我可以在close的方法参数中使用新特征的类型吗？

这是Scala中的多态性吗？

Answer 1

是的，当您定义具有共同特征的东西时，是一种多态性，简称为Subtype polymorphism 。

例，

scala> trait Compressor { def compress(data: String): String }
defined trait Compressor

scala> class Zipper extends Compressor { def compress(data: String) = s"$data is zip compressed" }
defined class Zipper

scala> class GZipper extends Compressor { def compress(data: String) = s"$data is gzip compressed" }
defined class GZipper

以特征为参数的方法，

scala> def compress (data: String, compressor: Compressor) = compressor.compress(data)
compress: (data: String, compressor: Compressor)String

scala> compress("i want to compress", new Zipper)
res1: String = i want to compress is zip compressed

斯卡拉的其他多态性是;

1. 参数多态-https: //stackoverflow.com/a/21115651/432903
2. 临时多态性-http: //blog.jaceklaskowski.pl/2015/05/15/ad-hoc-polymorphism-in-scala-with-type-classes.html

你可以学习coursera类周3（数据和抽象）的概念- https://www.coursera.org/learn/progfun1/home/week/3