初学者:Scala 2.10 中的 Scala 类型别名? [英] Beginner: Scala type alias in Scala 2.10?

问题描述

为什么此代码无法编译并显示错误:未找到:值矩阵?从文档和一些(可能已经过时的)代码示例来看，这应该可行吗?

Why does this code fail to compile with the error: not found: value Matrix? From the documentation and some (possibly out of date) code examples this should work?

object TestMatrix extends App{  
type Row = List[Int]
type Matrix = List[Row]


val m = Matrix( Row(1,2,3),
                Row(1,2,3),
                Row(1,2,3)
              )


}

推荐答案

Matrix 表示一种类型，但您将其用作值.

Matrix denotes a type, but you are using it as a value.

当你做List(1, 2, 3)时，你实际上是在调用List.apply，它是List.

When you do List(1, 2, 3), you are actually calling List.apply, which is a factory method for List.

要修复编译错误，您可以为Matrix 和Row 定义自己的工厂:

To fix your compiling error, you can define your own factories for Matrix and Row:

object TestMatrix extends App{  
  type Row = List[Int]
  def Row(xs: Int*) = List(xs: _*)

  type Matrix = List[Row]
  def Matrix(xs: Row*) = List(xs: _*)

  val m = Matrix( Row(1,2,3),
      Row(1,2,3),
      Row(1,2,3)
      )
}

这篇关于初学者:Scala 2.10 中的 Scala 类型别名?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！