Question

I would like an explanation of difference for example between this declaration:

class Clazz(param1: String, param2: Integer)

and this one:

class Clazz(param1: String)(param2: Integer)

Does second declaration affect just the way of instantiating the objects or is there any deeper reason I don’t know about.

One reason I thought about would be multiple variable length of parameters for example:

class Clazz(param1: String*)(param2: Integer*)

So are there any others?

Answer 1

#1 Type inference. It goes from left to right and is done per parameter list.

scala> class Foo[A](x: A, y: A => Unit)
defined class Foo

scala> new Foo(2, x => println(x))
<console>:24: error: missing parameter type
              new Foo(2, x => println(x))
                         ^

scala> class Foo[A](x: A)(y: A => Unit)
defined class Foo

scala> new Foo(2)(x => println(x))
res22: Foo[Int] = Foo@4dc1e4

#2 Implicit parameter list.

scala> class Foo[A](x: A)(implicit ord: scala.Ordering[A]) {
     |   def compare(y: A) = ord.compare(x, y)
     | }
defined class Foo

scala> new Foo(3)
res23: Foo[Int] = Foo@965701

scala> res23 compare 7
res24: Int = -1

scala> new Foo(new {})
<console>:24: error: No implicit Ordering defined for java.lang.Object.
              new Foo(new {})
              ^