SKB – Scala implicit conversion


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 implicit conversion.

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 implicit conversion !

Be careful ! I am going to show you something that you have to be really careful about.

With great power comes great responsibilities.

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


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 (2UnR8tnRRky1rrfT1MNDzw).

More information about Scala implicit conversion

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

The construct implicit def allows you to implicitly convert from one type to another.

The syntax is pretty straightforward:

implicit def [NAME](input: INPUT_TYPE): OUTPUT_TYPE = ???

It is usually named either from[INPUT_TYPE]To[OUTPUT_TYPE] or in our case since it is already contained inside of the companion object, simply to[OUTPUT_TYPE].

You have to be careful however. You can trap yourself.

For instance, if by mistake you are passing the name of the user in the id field, in a normal situation, the compiler would break and tell you that you are giving a String when the method expect an Int and that will catch your mistake.

However, let’s say you want to make your life easier for a different use case, you implement an implicit conversion that automatically convert String to Int. At this point, the compiler will automatically convert any String to Int which can create a real mess.

I would suggest to use implicit def extremely carefully and in very limited scope. Also, do not implement implicit conversion for basic types such as String or Int, but only for more complex types like trait or case class. So that you have a more refined control on when it is used.

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


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! 🙂

Leave a Reply

%d bloggers like this: