CODEWITHSUNDEEP
scala
EECOLOR
EECOLOR

Reputation: 11244

Function trait and implicit parameters

The following works:

object X extends (Int => String => Long) {

  def apply(x:Int):String => Long = ???
}

How could I type an apply function with an implicit parameter?

I have the following method:

def apply(x:Int)(implicit y:String):Long = ???

How can I describe the function type?

object X extends <functionType> {
  def apply(x:Int)(implicit y:String):Long = ???
}

update

I could define it like this:

object X extends (Int => String => Long) { 

  def apply(x:Int):(String => Long) = ???
  def apply(x:Int)(implicit y:String):Long = ???; 
}

But then calling it doesn't work:

error: ambiguous reference to overloaded definition,
both method apply in object X of type (x: Int)(implicit y: String)Long
and  method apply in object X of type (x: Int)String => Long
match argument types (Int)
              X(3)
              ^

Upvotes: 4

Views: 332

Answers (1)

ghik
ghik

Reputation: 10764

The only thing that comes to my mind is this:

object X {
  def apply(i: Int)(implicit y: String): Long = ???

  implicit def xToFun(x: X.type)(implicit y: String): Int => Long = x(_)
}

The implicit conversion will allow you to use X wherever Int => Long is needed, and the implicit String parameter will be resolved when that conversion is applied (not when X.apply is actually called):

val fun: Int => Long = X //error, no implicit String in scope

implicit val s = "fuu"
val fun: Int => Long = X //OK

Upvotes: 3

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