Mark existing variable as candiate for implicit method

Question

I try to write a method which should use a variable from the surrounding scope. The problem is that I cannot access the part of the code where the variable is defined. Something like this:

object Example extends App {

  val myvar = 1.0 // cannot change that code

  def myMethod()(implicit value:Double) = {
      print(value)
  }

  myMethod()
}

This fails because myMethod cannot find a suitable implicit for value.

is there a way to "mark" value as implicit after it has been defined, other than defining a new implicit variable pointing to value?

Background: We use Spark-Notebook where the SparkContext (named sc) is created automatically. As sc is a commonly known name for this variable in the community, we would prefer not to introduce another variable name.

Zlatoust

what's wrong with implicit val myvarAgain = myvar? – Molding

@EduardoParejaTobes I'd like not to introduce an additional variable... – Zlatoust

myMethod()(myvar) – Uncounted

What you want to do is to pass the spark context implicitly to a method? Why not explicitly? – Selective

(Spark Notebook dev here) If you really realliy need the implicit, consider changing the source code and making a custom build: github.com/andypetrella/spark-notebook/blob/master/conf/scripts/… – Selective

Answer 1

If you just don't want to have an instance of SparkContext that isn't labeled as sc you could assign it to an implicit-underscore variable like this:

implicit val _: SparkContext = sc

That would create an implicit variable of the correct type in scope for your function to use.

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Alternatively you can always pass implicit variables explicitly, in your example above you could do

myMethod()(myvar)

and that is the solution that I would use.

Souter

implicit val _ isn't an unnamed val. Its name is the underscore, and you can access it with back-ticks: println(`_`). (Does not work in the REPL) – Villeneuve

Cool thanks, I didn't know you could access it like that! I will edit my answer. – Souter