Scala: constructor with two paretneheses -

i'm new scala. following syntax mean?

case class user(val id: long)(val username: string) 

i've read currying in scala, explain please how related construction above (if related). thanks.

just partially-applied functions, constructor (which function arguments constructed type) can partially applied, in case:

scala> case class user(val id: long)(val username: string) defined class user  scala> val userbuilder = user(123l) _ userbuilder: string => user = <function1> 

note type of resulting userbuilder - it's function string (the remaining parameter) user

now, partially applied functions, can apply result string , user instance:

scala> val user = userbuilder("a") user: user = user(123)  scala> user.username res1: string = 

when useful?

1. when want construct many instances common values subset of arguments, e.g.:

   case class person(lastname: string)(val firstname: string)  class family(lastname: string, firstnames: list[string]) {   def getmembers: list[person] = {     val creator = person(lastname) _ // reused each first name!     firstnames.map(creator)   } } 

2. when want use 1 argument default value of one:

   case class measure(min: int)(val max: int = min*2)  measure(5)()   // max = 10 measure(5)(12) // default overridden, max = 12 

3. when want use implicit arguments, must reside in separate, last argument list of function, described int scala language specification (chapter 7.2):

a method or constructor can have 1 implicit parameter list, , must last parameter list given.