SBT FAQ: How do I set the desired Scala compiler version in the SBT build.sbt configuration file?
Set the value of the scalaVersion variable in your SBT build.sbt file. For instance, to use Scala 2.9.2, put an entry like this in the build.sbt file:
scalaVersion := "2.9.2"
To use Scala 2.10.0, put an entry like this in the build.sbt file:
Scala offers a cool feature where you can rename a class when you import it, including both Scala and Java classes. The basic syntax to rename a class on import looks like this:
import scala.collection.mutable.{Map => MMap}
and this:
import java.util.{HashMap => JavaMap}
If all you needed to know, I hope those "rename on import" syntax examples were helpful.
As a note to self, here are some ways to work with Dotty (Scala 3), SBT, and VS Code (Visual Studio Code).
Create a Dotty project:
sbt new lampepfl/dotty.g8
Launch VS Code inside that project directory, with Dotty support:
sbt launchIDE
Start SBT as usual:
sbt
Those notes are just a reminder for myself, but hopefully they’ll also help others work with Dotty, SBT, and VS Code.
I can never remember the name "unfiltered", so yesterday I kept trying to google for "web service framework", and to my surprise, Google wasn't showing unfiltered. In fact, it didn't show other tools like Scalatra, though it did show Play in the top ten.
So today's post is an effort to help Google out a little bit here. If you're looking for good Scala web service frameworks, check out these tools:
I normally don’t like to have sales on my books, but the short story is that the PDF version of Functional Programming, Simplified is currently on sale for $15.
As a brief note to self, if you ever want to write some code using Scala that recursively descends through a directory tree, here’s a solution that uses the Java SimpleFileVisitor and Files.walkFileTree method. First, here’s a skeleton class for the SimpleFileVisitor part of the solution:
If Functional Programming, Simplified seems large, a) I intentionally wrote it in a simple, leisurely style, and b) it’s a lot easier than reading hundreds of blog posts and all of those books on the right (although a few of those books are really good).
November 26, 2019: The PDF version of my book “Hello, Scala” is now free, and you can download it by clicking on the image below.
Future “updated and improved” versions of the book are being released as Scala Book. Currently an HTML version of the book is available here on the scala-lang.org website, and we’ll have PDF, MOBI, and ePub versions of that available once the creation process is automated and a few other issues are resolved.
But for now, click on the image below if you’d like to download the PDF of Hello, Scala for free:
My MacBook recently told me I was running out of disk space. I knew that the way I was backing up my iPhone was resulting in me having multiple copies of photos and videos, so I finally decided to fix that problem by getting rid of all of the duplicate copies of those files.
So I wrote a little Scala program to find all the duplicates and move them to another location, where I could check them before deleting them. The short story is that I started with over 28,000 photos and videos, and the code shown below helped me find nearly 5,000 duplicate photos and videos under my ~/Pictures directory that were taking up over 18GB of storage space. (Put another way, deleting those files saved me 18GB of storage.)
Just fooling around a little bit at the moment, here are several ways to write for/do blocks with the “significant indentation” style in Dotty (Scala 3) as of Dotty v20:
Here’s some source code that demonstrates a quiet, concise, and attractive new programming language I’d enjoy using:
SALE: I’ve lowered the price of the PDF version of Functional Programming, Simplified to $20 for the 2019 holiday season. I don’t know when I’ll increase it again, but the usual selling price is as high as $35.
As a relatively brief note, this seems to be the correct way to start a Play Framework application as a service on an Ubuntu 16.04 system.
First, you need to create a little Unix shell script that runs the startup command for your Play Framework application. I created a Play application for a website named kbhr.co, so I cd into the directory for that website:
I’ll write about this a little more when I’m awake, but here’s a little look at ADTs implemented in Scala 2 (with traits and case objects) and Scala 3 enums.
One small step for me, and I don’t know if it will help mankind at all. But Hello, Scala is now called Scala Book, and you can find it here on scala-lang.org.
When I originally saw the first image, I thought it was a “This would be nice in Scala 3 (Dotty)” idea. But then I found the “No parentheses in control structures” pull request shown in the second image. Here’s a link to that pull request.
“I though it was obvious, but apparently it's not. FP is not about not having side effects at all, otherwise it would be useless. It's just about deferring them for as long as possible, that's all.”
~ Alessandro Lacava, in this tweet
As a brief note today, I found that GraalVM was actually making one of my Scala/Java/JVM applications slower, so with the help of Thomas Wuerthinger at Oracle, I learned a little bit about how to use the GraalVM profile-guided optimizations.
I was having a bear of a time trying to understand how to set the default indentation when editing Scala files using Microsoft Visual Studio (VS) Code, but I finally found the solution. The short story is that you want to edit the settings.json file, and add the code that I’ve made bold here:
Motivated by GraalVM, I rewrote my sbtmkdirs command using Scala. Here’s a link to the new Scala `sbtmkdirs` project on Github.