Scala and @Inject annotation

Question

I know that the best way to deal with dependency injection in Scala is using tools that were built specifically for the language, but I working on a project that must integrate some Scala and Java code.

Then, I am using Google Guice, that implements specification JSR-330. Fortunatly, I found no problem during integration of Guice and Scala. I am using constructor injection, because I have to deal with immutability.

My question is, why in Scala we have to use the notation @Inject() in front of the constructor parameter? Why the () paranthesis? It follows an example:

class MyClass @Inject() (val another: AnotherClass) {
  // Body of the class
}

Answer 1

Otherwise, how could you tell if (val another: AnotherClass) is constructor parameter list or arguments to @Inject?

Answer 2

It is all about the syntax of annotating a constructor. Scala requires a constructor annotation to have one (and exactly one) parameter list (even if it is empty)

class Bar @Fooable() ( val i : Int) {

}

What would the i parameter belong to below: The annotation or the Bar class?

class Bar @Fooable( val i : Int) {

}