Question

I am trying to figure out how to create a method that takes a nested object as an argument. For a nested class I can do the following:

scala> class Outer { 
 | class Inner
 | def method(i:Outer#Inner) = { "inner class" }
 | }
defined class Outer

However, if I try something like that with an object instead i get an error:

scala> class Outer { 
 | object Inner
 | def method(i:Outer#Inner) = { "inner object" }
 | }
<console>:11: error: type Inner is not a member of Outer
   def method(i:Outer#Inner) = { "inner object" }

What should the type of the argument to the method be to accomplish this? Also I want to refer to the type of Inner object not generalize the argument to say Any.

Answer 1

Inneris an object, thus it is not a type, and can’t be use as a type. the type of Inner is Inner.type. It means, in your example. Unfortunately, each instance of Outer will have it’s own Inner object and type Outer#Inner.type can not be used, since it is not stable. A workaround is to use: this.Inner.type.

 def method(i:this.Inner.type) = { "inner object" }

But it means that you can only pass as a parameter the Inner object of the instance on which you call method.