Scala 中的类型定义
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Typedef in Scala
提问by Aleksandr Pakhomov
How can I define type in Scala? Like
如何在 Scala 中定义类型？喜欢
type MySparseVector = [(Int, Double)]
in Haskell or
在 Haskell 或
typedef MySparseVector = std::list<std::pair(int, double)>>
in C++?
在 C++ 中？
I tried
我试过
type MySparseVector = List((Int, Double))
but can't figure how to make it work. If I write this in the beginning of class file I got "Expected class or object definition" error.
但不知道如何使它工作。如果我在类文件的开头写这个，我会收到“预期的类或对象定义”错误。
PS Sorry, I mistyped. I tried to use List[(Int, Double)] in Scala.
PS对不起，我打错了。我尝试在 Scala 中使用 List[(Int, Double)] 。
回答by y?s??la
type MySparseVector = List[(Int, Double)]
Example usage:
用法示例：
val l: MySparseVector = List((1, 1.1), (2, 2.2))
Types have to be defined inside of a class or an object. You can import them afterwards. You can also define them within a package object - no import is required in the same package, and you can still import them into other packages. Example:
类型必须在类或对象内定义。您可以稍后导入它们。您还可以在包对象中定义它们 - 在同一个包中不需要导入，您仍然可以将它们导入到其他包中。例子：
// file: mypackage.scala
package object mypackage {
type MySparseVector = List[(Int, Double)]
}
//in the same directory:
package mypackage
// no import required
class Something {
val l: MySparseVector = Nil
}
// in some other directory and package:
package otherpackage
import mypackage._
class SomethingElse {
val l: MySparseVector = Nil
}
