Posts in the “scala” category

My 100% FREE “Introduction to Functional Programming” online video training course is now finished! To make things a little easier, here are links to all of the free videos in the training course:

March 24, 2024: I just released my free “Advanced Scala 3” online video training course. This free video course gets into different Scala programming topics such as functions, types, generics with variance and bounds, multiversal equality, modular programming, extension methods, and much more.

As always I want to thank Ziverge’s software consulting services for sponsoring these videos! These video courses take many weeks and even months to create, and they would not exist without Ziverge.

<<Click here to start my free Advanced Scala 3 video training course.>>

April, 2024: As a brief note today, the PDF version of my book, Learn Functional Programming The Fast Way!, is now FREE. I wrote this functional programming book for Scala, Java, and Kotlin developers, and you can now download it for free here:

• Learn Functional Programming The Fast Way! (free PDF)

If you’re interested in functional programming, or just want to learn more about data types, generics, pure functions, expression-oriented programming, and functional error handling, I hope this book is helpful.

Scala FAQ: When compiling a Scala application with SBT, I get warning messages like these:

$ sbt compile

[warn] there were 6 deprecation warnings; re-run with -deprecation for details
[warn] there were 4 feature warnings; re-run with -feature for details

How do I ’re-run with -deprecation’ or ’re-run with -feature’?

Summary: This post is a discussion of the “Option/Some/None Pattern” in Scala, specifically how to use the Either/Left/Right data types instead of Option when you need to know the reason some code failed. As you may know, the None data type does not return failure/exception information, but if you use the Either/Left/Right types, you can access that failure information through the Left type.

The post is sponsored by my book, the 2nd Edition of the Scala Cookbook.

Scala List FAQ: Can you share some Scala List class examples?

The Scala List class may be the most commonly used data structure in Scala applications. Therefore, it's very helpful to know how create lists, merge lists, select items from lists, operate on each element in a list, and so on.

In this tutorial, I'll share examples of the most common List operations (methods).

This is a “cheat sheet” for the Scala 3 programming language. I initially wrote it for my book Learn Functional Programming The Fast Way, but I thought I’d share it here as well.

If you want to see many more details about Scala 3, see:

• The free, online Scala 3 Book (which I co-wrote)
• My book, Learn Scala 3 The Fast Way!
• The Scala Cookbook (2nd Edition)
• Functional Programming, Simplified
• My free 115-page e-book, Learning Recursion

If you ever need some good ScalaJ-HTTP examples, see the test files in the project, including this HttpBinTest.scala file. That file currently shows a number of good ScalaJ-HTTP examples, including GET, POST, and redirect examples with Scala.

See that page for a full list of examples, but for my own use, here are a few of them.

Scala FAQ: Can you show an example of the Scala 3 if-then-else-if syntax?

Scala 3 solution

Here’s an example of the Scala 3 if-then/else-if/else syntax, as used as the body of a method:

I ran into a strange problem this weekend where I noticed a huge difference between the way a Scala Future and a Thread worked for the exact same code. I think I’m pretty aware of the obvious differences between futures and threads, so this really caught me by surprise. If/when I figure out why there was such a difference in behavior for the given problem I’ll post that information here.

A Scala Thread example

While that problem will haunt me for a while, what I really want to post here today is a simple Scala Thread example:

As a brief note today, this is a very little ZIO HTTP Server application. I’m sharing it here because it’s currently a fairly simple example, and also because I show how to include the necessary ZIO dependencies using Scala-CLI:

Scala collections FAQ: How can I convert a Scala array to a String? (Or, more, accurately, how do I convert any Scala sequence to a String.)

A simple way to convert a Scala array to a String is with the mkString method of the Array class. (Although I've written "array", the same technique also works with any Scala sequence, including Array, List, Seq, ArrayBuffer, Vector, and other sequence types.)

Scala FAQ: Can you share some examples of the Scala if/then/else syntax? Also, can you show a function that returns a value from an if/then/else statement?

In its most basic use, the Scala if/then/else syntax is very similar to Java:

A powerful Scala idiom is to use the Option class when returning a value from a function that can be null. Simply stated, instead of returning one object when a function succeeds and null when it fails, your function should instead return an instance of an Option, where the instance is either:

1. In the success case, return an instance of the Scala Some class
2. In the failure case, return an instance of the Scala None class

Because Some and None are both children of Option, your function signature just declares that you're returning an Option that contains some type (such as the Int type shown below). At the very least, this has the tremendous benefit of letting the user of your function know what’s going on.

I've been trying to find some good Scala currency and money libraries lately, and I just ran across the following list of projects on the Joda Money Github project. That URL contains the following list of Java and JVM-based projects that should all be usable in Scala:

If you’d ever like to pay it forward — or in this case, backwards — all of my free Scala and functional programming video training courses are sponsored by Ziverge, and if you ever need to supplement your development team, please see their On-Demand Team Extension Service. They have qualified developers that work with Scala, Rust, artificial intelligence, and many other technologies.

Scala FAQ: How do I perform pattern matching on a regular expression string in a match expression?

Using Scala 3, I was just trying to perform some pattern matching on a regular expression (regex) string in a match expression, and while working with ChatGPT, I came up with this solution, which you can easily verify in the Scala REPL:

Here’s a brief Scala 3 example that shows how to:

1. Create a companion object,
2. Create an apply method in that companion object that acts as a factory method,
3. Define that apply method to take a varargs tuple parameter, and
4. Create new Person instances using that factory method.

Here’s the complete source code for this example:

Scala FAQ: How do I get the current month as an integer or as a string in Scala?

Solution