Scala Cookbook

19.8. Building Functionality with Types

To put what you’ve learned in this chapter to use, let’s create two examples. First, you’ll create a “timer” that looks like a control structure and works like the Unix time command. Second, you’ll create another control structure that works like the Scala 2.10 Try/Success/Failure classes.

Example 1: Creating a Timer

On Unix systems you can run a time command (timex on some systems) to see how long commands take to execute:

$ time find . -name "*.scala"

That command returns the results of the find command it was given, along with the time it took to run. This can be a helpful way to troubleshoot performance problems.

You can create a similar timer method in Scala to let you run code like this:

val (result, time) = timer(someLongRunningAlgorithm)
println(s"result: $result, time: $time")

In this example, the timer runs a method named longRunningAlgorithm, and then returns the result from the algorithm, along with the algorithm’s execution time. You can see how this works by running a simple example in the REPL:

scala> val (result, time) = timer{ Thread.sleep(500); 1 }
result: Int = 1
time: Double = 500.32

As expected, the code block returns the value 1, with an execution time of about 500 ms.

The timer code is surprisingly simple, and involves the use of a generic type parameter:

def timer[A](blockOfCode: => A) = {
  val startTime = System.nanoTime
  val result = blockOfCode
  val stopTime = System.nanoTime
  val delta = stopTime - startTime
  (result, delta/1000000 ...