什么是List [String~Int]？

Question

While going through the scala documentation ( Play Docs ) of the play framework I saw a syntax I have never seen before.

val populations:List[String~Int] = {
  SQL("select * from Country").as( str("name") ~ int("population") * ) 
}

Could someone please tell me what does "~" in List[String~Int] mean?

Answer 1

May be this willl help:

scala> class ~[A, B]
defined class $tilde

scala> List.empty[String~Int]
res1: List[~[String,Int]] = List()

Actually, ~ is not a part of the standard library, this is a generic class from the play framework, which allows an infix notation. In scala, any generic class that takes 2 generic parameters can be use with an infix notation. for example, the following also works:

scala> class X[A, B]
defined class X

scala> List.empty[String X Int]
res1: List[X[String,Int]] = List()

In your case, you will find the definition of ~ in the Play framework API .