Typedef in Scala

Question

How can I define type in Scala? Like

type MySparseVector = [(Int, Double)] 

in Haskell or

typedef MySparseVector = std::list<std::pair(int, double)>>  

in C++?

I tried

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.

PS Sorry, I mistyped. I tried to use List[(Int, Double)] in Scala.

Answer 1

type MySparseVector = List[(Int, Double)] 

Example usage:

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:

// 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 }