How do I use a structural type with generic parameters?

Question

I have two case classes

case class StringCaseClass(argument: String)

case class IntCaseClass(argument: Int)

I want to define a structural type which will match the companion object of both of these

type HasApply1 {
  def apply[A, R](argument: A): R
}

This will compile fine, but when I try to use it like this

def method(caseClass: HasApply1) {
  // whatever
}

method(StringCaseClass)

I will get a compiler error

found   : StringCaseClass.type
required: WithApply1
            (which expands to)  AnyRef{def apply[A, R](string: A): R}

Is there any way of accomplishing this? If I redefine the structural type to have concrete types for A and R it will compile correctly, but then I lose the flexiblity

Answer 1

@aloiscochard's comment is almost there. What he forgot to mention is that case class companion objects already implement the appropriate FunctionN trait, so you can simply do this,

scala> case class StringCaseClass(argument: String)
defined class StringCaseClass

scala> case class IntCaseClass(argument: Int)
defined class IntCaseClass

scala> def method[A, R](caseClass: A => R, a: A) = caseClass(a)
method: [A, R](caseClass: A => R, a: A)R

scala> method(StringCaseClass, "foo")
res0: StringCaseClass = StringCaseClass(foo)

scala> method(IntCaseClass, 23)
res1: IntCaseClass = IntCaseClass(23)