What is "type" of a function with implict?

Question

Let's say I have a function with a signature like this:

 def tsadd(key: Any, time: Double, value: Any)(implicit format: Format): Option[Int]

And I want to create a list of some number of these functions for later evaluation. How do I do it. I tried creating a list like:

val pipelineCmds:List[(String,Double,Any)(Format) => Option[Int]] = Nil

and doing this:

pipelineCmds ++ r.tsadd(symbol, timestamp.getMillis.toDouble, value)

But the val didn't respond well the implicit param Format. It expects to see a ] after the first set of parens.

The ultimate goal is to do something like

r.pipeline { p => 
  pipelineCmds.foreach(c => p.c)
}

Any help is greatly appreciated!

Answer 1

As far as I know, functions with implicit parameters are annoying to work with. The appropriate types are (your choice):

(String, Double, Any) => Format => Option[Int]    // As written
Format => (String, Double, Any) => Option[Int]    // Conceptually works more like this
String => Double => Any => Format => Option[Int]  // Completely curried
(String, Double, Any, Format) => Option[Int]      // Closest to how the JVM sees the method

but partial application of the function does not work well. You can annoyingly annotate all your types to get the last version:

class Format {}   // So the example works
def tsadd(s: String, d: Double, a: Any)(implicit f: Format): Option[Int] = None
scala> tsadd(_: String, _: Double, _: Any)(_: Format)
res2: (String, Double, Any, Format) => Option[Int] = <function4>

but it's not much harder to write your own to be whatever shape you want:

def example(f: Format => (String, Double, Any) => Option[Int]) = f
scala> example(f => { implicit val fm=f; tsadd _ })
res3: (Format) => (String, Double, Any) => Option[Int] = <function1>

Of course, if you already know the implicit values when you're creating the list, you just need the type

(String, Double, Any) => Option[Int]

and you assign the functions like

tsadd _

Answer 2

scala> val pipelineCmds:List[(String,Double,Any) => Format => Option[Int]] = Nil
pipelineCmds: List[(String, Double, Any) => (Format) => Option[Int]] = List()

But note that the "implicitness" is lost from function values and you must explicitly pass in a format.