Which case will use implicit parameter and multi parameter in Scala

Question

I had some code:

def sum1(x: Int)(y: Int) = x + y

and

def sum2(x: Int)(implicit y:Int) = x + y

Could you please explain for me which case will use sum1 and sum2?

Thank you!

Answer 1

In order to call a function with an implicit parameter, exactly one value with a type matching the implicit parameter must exist in the implicit scope.

Here are some very easy examples:

def implicitSum(n: Int)(implicit m: Int): Int = n + m

val a = {
  implicit val a = 2
  implicitSum(1) // equals 3
}

val b = {
  implicit val b = 3
  implicitSum(1) // equals 4
}

val c = {
  implicit val c = 4
  implicitSum(1)(1) // equals 2: explicit parameter has higher priority
}

val d = {
  implicitSum(1) // does not compile, no implicit (or explicit) parameter
}

As you may understand from the examples, implicit resolution is done at compile time.

To know more on the topic (and to have some more interesting and meaningful examples) I suggest reading this page of the Scala documentation.