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.
Scala String FAQ: How do I split a String in Scala based on a field separator, such as a String I get from a comma-separated value (CSV) file or pipe-delimited file.
Use one of the split methods that are available on Scala/Java String objects. For instance, this example in the Scala REPL shows how to split a string based on a blank space:
Scala FAQ: How do I sort a sequential collection in Scala? (Or, how do I implement the Ordered trait in a custom class so I can use the sorted method (or operators like <, <=, >, and >=) to compare instances of my class?
I just found some notes from when I first began working with Scala, and I was working with the yield keyword in for loops. If you haven't worked with something like yield before, it will help to know how it works. Also, when you need to do searches for problems, or when you want to talk to other Scala developers, it will also help to know that when you use the for/yield keywords as shown in these examples, you’re creating something known as a for expression.
Here's a statement of how the yield keyword works in for loops, from the book, Programming in Scala:
I’ve known about using Scala’s zipWithIndex method for quite some time. I used it in for loops to replace counters, and it works like this:
scala> List("a", "b", "c").zipWithIndex
res0: List[(String, Int)] = List((a,0), (b,1), (c,2))
I learned about using zip with Stream last night while reading Joshua Suereth’s book, Scala In Depth. It works like this:
This page contains a collection of over 100 Scala String examples, including string functions, format specifiers, and more. I don’t provide too many details about how things work in these examples, although I do show the output of all the examples. This is mostly just a collection of examples that can be used as a Scala String reference page or cheat sheet.