SKB – Scala pattern matching

SKB – Scala pattern matching

Introduction

This article is part of the Scala knowledge bits Series.

Periodically, I will publish new exercises so you can slowly build up knowledge about Scala.

It is designed to be done in a very short amount of time and learn a little bit each day, just to create a routine.

This episode will teach you about Scala pattern matching.

Hope you are going to enjoy it! It is designed for anyone to learn Scala from scratch and slowly learn, one Bit at a time.

After this Bit, I would love to hear your feedback in the comments down below.

Feel free to join the Discord server as well if you would like some help and support from the rest of our community.

What are we learning today?

Today we are going to learn about Scala pattern matching !

We are going to learn about pattern matching today. At least, an introduction. Pattern matching is one of the key functionality of scala and it contributes to help you write clean and readable code.

Time to try on the exercise on your own and scroll down for more information when you are done or if you are stuck.

Exercise

Here is an exercise to complete today.

If I did my job well, you should be able to guess by yourself the solution based on what you previously learned and based on the clues.

But if you get stuck, scroll down to get more information.

The goal of the exercise is to replace the ??? by a piece of code so that the exercise compiles and that’s how you win! Good luck!

You can fill the exercise right in here:

Or, if it does not load, go on to Scastie (5VQri4WFQ6yrPuBJHNIh5A).

More information about Scala pattern matching

In this exercise you will learn (or have learned, if you have already solved the puzzle) about Scala pattern matching.

The main keyword to use pattern matching is match. But as you saw, you can also use it inside map, as well as flatMap and filter and more.

The overall syntax is:

value match {
    case holder => action
    case _ => default case
}
And similar inside a map or other:
list.map {
    case holder => action
    case _ => default case
}

It works kind of like a switch in other languages. And similar to switch, the case are evaluated in order, the first one that evaluate to true will be executed and none of the other ones will be.

There are plenty of ways that pattern matching can be used and we only saw a few here, let’s review:

  • catch all: case n => ???
  • catch all without the value: case _ => ???
  • With condition: case n if n % 2 == 0 => ???
  • Exact match: case 3 => ??? or case "abc" => ???
  • List extraction:
    • Empty list: case Nil => ???
    • Extract head: case head :: tail => ???
    • One element: case head :: Nil => ???
    • Two elements: case first :: second :: Nil => ???
    • One element with condition: case head :: Nil if head % 2 == 0 => ???
    • Extract value: case 12 :: tail => ???
  • With types: case n: String => ???
  • Case classes: (there will be an SKB about it)
    • Extraction of field: case Person(firstName, lastName) => ???
    • Extraction of field with condition: case Person(firstName, lastName) if firstName.startsWith("L") => ???
    • Extraction of field with exact match: case Person("Leo", lastName) => ???
  • With regex: There will be an SKB about it
  • With Scala version of enumeration: There will be an SKB about it
I might have forgotten some. If so, please let me know in the comment below or on our discord server.

Feel free to go back to the exercise, modify the code to try out new things and get a better intuition for Scala pattern matching.

Conclusion

I hope you have learned something new or had fun during this Scala Knowledge Bit.

Please ask questions or post feedback in the comments below.

Feel free to try on the next Scala Knowledege Bit.

If you are curious about the previous Scala knowledge Bits, go check it out! 🙂

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