The need to write a pattern-matching decomposition when mapping over a sequence of tuples has always annoyed some Scala developers. So many might appreciate this new feature.

Consider you have a list of pairs

val pairs = List(1, 2, 3).zipWithIndex
// pairs: List[(Int, Int)] = List((1,0), (2,1), (3,2))

Imagine you want to map pairs to a list of Ints so that each pair of numbers is mapped to their sum. The best way to do this in Scala 2.x was with a pattern matching anonymous function.

pairs map {
  case (x, y) => x + y
}
// res1: List[Int] = List(1, 3, 5)

Scala 3 now allows us to write

pairs map {
  (x, y) => x + y
}
// val res0: List[Int] = List(1, 3, 5)

or

pairs.map(_ + _)
// val res1: List[Int] = List(1, 3, 5)

• We can apply the new way of encoding in several places in the source code.

• Have a look for them in the following files:

  • ReductionRules.scala
  • SudokuProblemSender.scala
  • SudokuProgressTracker.scala
  • SudokuSolver.scala
  • TopLevelDefinitions.scala (we chose to put the content of the package object in a file with this name.)

• Identify them and replace the pattern-matching syntax with the new syntax

• Run the provided tests by executing the test command from the sbt prompt and verify that all tests pass

• Verify that the application runs correctly

After successfully completing the tasks in this exercise, move to the next one by running the cmtc next-exercise from the command line.

scalafmt based source code formatting is in place in this project. scalafmt supports both Scala 2 and Scala 3. You can [re]format the code by running scalafmtAll from the sbt prompt. As we switch from Scala 2 to Scala 3, you need to make sure that a matching scalafmt configuration is in place. In any of the exercises, you can run cmtc pull-template .scalafmt.conf to "pull-in" the correct configuration file.

The font size can be a bit too small for the taste of some people. You can change the Markdown zoom setting in IntelliJ by pasting the following CSS snippet in the markdown setting in " Settings" -> "Languages & Frameworks" -> "Custom CSS -> CSS rules" and adjust the font-size setting to your liking:

body {
  font-size: 120% !important;
  }