初学者：Scala 2.10 中的 Scala 类型别名？
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Beginner: Scala type alias in Scala 2.10?
提问by Tony
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 From the documentation and some (possibly out of date) code examples this should work?
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，这应该有效吗？
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)
)
}
回答by Régis Jean-Gilles
Matrixdenotes a type, but you are using it as a value.
Matrix表示一种类型，但您将其用作值。
When you do List(1, 2, 3), you are actually calling List.apply, which is a factory method for List.
当您这样做时List(1, 2, 3)，您实际上是在调用List.apply，这是List.
To fix your compiling error, you can define your own factories for Matrixand Row:
要修复编译错误，您可以为Matrixand定义自己的工厂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)
)
}
回答by korefn
From thisarticle you have.
从这篇文章你有。
Note also that along with most of the type aliases in package scala comes a value alias of the same name. For instance, there's a type alias for the List class and a value alias for the List object.
还要注意，与包 scala 中的大多数类型别名一起出现的是同名的值别名。例如，List 类有一个类型别名，List 对象有一个值别名。
A solution to the problem translates to:
该问题的解决方案转化为：
object TestMatrix extends App{
type Row = List[Int]
val Row = List
type Matrix = List[Row]
val Matrix = List
val m = Matrix( Row(1,2,3),
Row(1,2,3),
Row(1,2,3))
}
