Given the following code:

object Quizful {
  def main(args: Array[String]) {
    println(s"Delayed time: ${delayed(time())}")
  }

  def time() = {
    println("Getting time in nano seconds")
    System.nanoTime
  }
  def delayed( t: => Long ) = {
    println("In delayed method")
    println("Param: " + t)
    t
  }
}

What will be printed into the console after running this programm?

In delayed method
Getting time in nano seconds
Param: 3026149960356229
Getting time in nano seconds
Delayed time: 3026149960537279
Getting time in nano seconds
In delayed method
Param: 3026073159375008
Delayed time: 3026073159375008
In delayed method
Param: 3026149960356229
Getting time in nano seconds
Delayed time: 3026149960537279
Delayed time: 3026149960537279
In delayed method
Getting time in nano seconds
Param: 3026149960356229
Getting time in nano seconds
Delayed time: 3026149960537279
In delayed method
Getting time in nano seconds
Param: 3026149960356229

Explanation

A call-by-name mechanism passes a code block to the callee and each time the callee accesses the parameter, the code block is executed and the value is calculated.
Here, we declared the delayed method, which takes a call-by-name parameter by putting the => symbol between the variable name and the type. When the above code is compiled and executed, it produces the following result:

C:/>scalac Quizful.scala
C:/>scala Quizful
In delayed method
Getting time in nano seconds
Param: 3026149960356229
Getting time in nano seconds
Delayed time: 3026149960537279

C:/>

Here, delayed prints a message demonstrating that the method has been entered. Next, delayed prints a message with it's value. Finally, delayed returns t.
Read more: Scala Functions Call-by-Name