ZIO/ZLayer FAQ: How do I use a Typesafe Config HOCON properties file with ZIO?
For this ZIO ZLayer solution, you can use the zio-config library for things like this, but at the moment my preferred approach is to hand-code this solution. That’s probably because I’ve written code before to read a HOCON file, so it’s more straightforward atm.
If you’re interested in this sort of thing, I’ve been trying to fix the pages for my free Scala and functional programming video courses, and to that end I needed to do some things with reading HOCON configuration files, and screen-scraping of my own website pages.
Therefore, without much explanation, here is some source code that I wrote over the last day or two, with the help of an A.I. tool or two. One thing to note is that the quality of the code isn’t very good, because I let the A.I. tools generate most of it, and I didn’t bother to clean it up.
As a little Scala note today, here are a few links to some ZIO — ZIO 2 — training videos I have released recently:
I’ll release an entire ZIO 2 video training course soon, so please stay tuned for that.
If you’re ever in Mt. Sterling, Kentucky, one of my nieces owns a used bookstore named Mooncat Book Company, and she now has three signed copies of the Scala Cookbook. :)
My free “Introduction to Functional Programming” video course is almost complete. Today I released 12 new lessons, starting with for Loops, Generators, and Guards, and ending with Lessons Learned.
After this there are about five final lessons (depending on what I decide to include), and by the end of the course we’ll start writing some ZIO code.
As always, many thanks to Ziverge’s Scala and Rust consulting services for sponsoring the creation of these “100% Free” videos, with no ads and no firewalls!
I’m pleased to announce that my 100% Free “Introduction to Scala 3” video training course is now online. I say it’s 100% Free because there are no ads and no paywalls — just free Scala 3 training videos.
This video training course is free thanks to Ziverge, which is sponsoring my work.
March 26, 2024 Update: As a brief note today, here are links to my new, free online video training courses:
As always, these videos are sponsored by Ziverge software consulting (specializing in Rust, Scala, and ZIO).
January 15, 2024: I just released 15 new videos for my free “Introduction to Functional Programming” video course. The new videos start with this Try, Success, Failure video, and get into developing the second application
If you’re ever at the SBT command line and want to limit the number of compiler errors shown by the compile task, this command sets the maximum number of errors outputted to 5:
Scala performance FAQ: Is there a reliable way to determine the number of processors (CPUs) or cores when writing Scala code?
As I was reading this article on ZIO performance tuning, I decided to look into whether there is a reliable way to determine the number of CPUs or cores on a computer using Scala (and therefore Java, Kotlin, and other JVM languages).
The solution is that there seems to be a reliable way to determine the number of CPUs or cores in Scala. In short, use the Java Runtime class to get the information. This Scala example shows how to do it:
As a brief note today, here’s a little ZIO 2 example that shows how to print a series of values with a random delay in between each value that’s printed.
Also note that in the code below there are different ways to implement randomWaitTimeInSeconds ... for instance, it could return a Duration, but I just have it return an Int.
I also use ZIO.foreach to generate the values in a range, and that could be handled differently.
Another thing I do is use an exception inside ZIO.fail, and I do that because I want that error to be a Throwable on the ZIO “error channel” (i.e., the E parameter in ZIO[R, E, A].)
ZIO 2 FAQ: How do I work with the ZIO.attempt function?
When you’re working with existing (legacy) Scala code that:
wrap that code with ZIO.attempt. As you’re about to see, this creates a ZIO effect from that legacy code.
Not only does this create a ZIO effect, it also puts the exception in the ZIO “error channel,” i.e., the E parameter in the ZIO[R, E, A] type signature.
As I wrote in my ZIO “mental model” and best practices article, when I work with ZIO, I like to separate (a) my application from (b) the ZIO run value. Specifically I mean that I like to handle the results of the application in the run value. (If you’ve read my previous ZIO blog posts, when I say “application,” I mean our main equation or blueprint.)
There are quite a few different ways to write a ZIO run value, and in this tutorial I want to show many of the different ways I know, or at least those I can remember today. :)
Scala FAQ: Can you share some examples of using tuples in Scala?
A Scala tuple is a class that can contain a miscellaneous collection of elements. I like to think of them as a little bag or container you can use to hold things and pass them around.
You create a tuple with the following syntax, enclosing its elements in parentheses. Here's a tuple that contains an Int and a String:
In this ZIO performance tuning article by Pierre Ricadat, there’s this nice tip about using ZIO.foreachDiscard instead of ZIO.foreach:
“One of ZIO's common operators is ZIO.foreach, which allows you to run an effect for each item in a collection. There's also ZIO.foreachDiscard that is faster if you don't need to collect results (e.g., if your effect returns Unit).”
For more details, see that article.
Here’s a quick Scala example that shows how to convert multiple spaces in a string to a single space:
scala> val before = " foo bar baz bonk "
before: String = " foo bar baz bonk "
scala> val after = before.trim.replaceAll(" +", " ")
after: String = foo bar baz bonk
As a “note to self” as much as anything, I just updated the following Scala videos and/or video pages:
I had a small issue with these pages, and I think that issue is now corrected.
As I’ve been learning more about Scala and functional programming, I’ve been looking at accomplishing more tasks with recursive programming techniques. As part of my studies, I put together a number of Scala recursion examples below, including:
Note: The following examples of passing a function as an argument to another function have all been taken from the PDFs on the Scala website. The only thing I've done here is to add comments to the source code, and add detailed discussions of them in this article.