Scala lambda in function args-CodePudding

I have some code block like this:

object EntryPoint extends App {

  val arr = ArrayBuffer(1, 2, 3)
  doFirst(arr)

  def doFirst(a: ArrayBuffer[Int]) = {
    doSecond(s"$a")
  }

  def doSecond(
                 x: => String = ""
                 ) = {
    x match {
      case s: String => println(s"This is string: $s")
      case _ => println(x.getClass.getName)
    }
  }
}

Output: This is string: ArrayBuffer(1, 2, 3)

Why x evaluated like a string if in debugger i see lambda with 3 arguments? Is it because every call x is x.apply() ?

CodePudding user response：

A by-name parameter like x: => String is conceptually the same as a function with signature () => String

The following are equivalent and as you noticed already both parameters end up with the same runtime representation when debugging.

def doWithByNameParam(x: => String): String =
    x

def doWithFunction(x: () => String): String =
    x.apply()

doWithByNameParam("string")
doWithFunction(() => "string")

You just avoid some boilerplate with doWithByNameParam

Later Edit:

Here's what javap will give just so you understand what happens under the hood

  public static java.lang.String doWithByNameParam(scala.Function0<java.lang.String>);
  public static java.lang.String doWithFunction(scala.Function0<java.lang.String>);