scala 2

A small Scala 2 project converted to Dotty

If you want to see a somewhat larger example of Dotty source code than I’ve shown before, I just took a little time to convert a small Scala 2 project over to the new/current Dotty syntax (i.e., the Dotty syntax supported by the Dotty 0.21 release, circa January, 2020).

Examples of converting Scala 2 code to Scala 3 with Dotty 0.20

Table of Contents1 - Significant indentation syntax with traits and classes2 - match expressions3 - for loops and if/else (and `do` and `then`)4 - try/catch syntax5 - A couple of braces not removed6 - More Dotty/Scala 3 changes

With the Dotty compiler you can convert Scala 2 code to the new Scala 3 syntax, and with the Dotty 0.20.0-RC1 release on November 4, 2019, I thought I’d see how some of the conversions work. Almost all of the changes shown below have to do with the elimination of curly braces and the use of “significant indentation” syntax, but in one example I also show the then and do keywords.

Implicit methods/functions in Scala 2 and 3 (Dotty extension methods)

Table of Contents1 - Scala 2: Create the method in an implicit class2 - Scala 3 (Dotty): Adding methods to closed classes with extension methods3 - Discussion (Dotty syntax)4 - Where to put Dotty extension methods

Scala lets you add new methods to existing classes that you don’t have the source code for, i.e., classes like String, Int, etc. For instance, you can add a method named hello to the String class so you can write code like this:


which yields output like this:

"Hello, Joe"

Admittedly that’s not the most exciting method in the world, but it demonstrates the end result: You can add methods to a closed class like String. Properly (tastefully) used, you can create some really nice APIs.

In this article I’ll show how you can create implicit methods (also known as extension methods) in Scala 2 and Scala 3 (Dotty).