Posts in the “scala” category

Scala FAQ: When you create a case class in Scala, a copy method is generated for your case class. What does this copy method do?

In short, it lets you make a copy of an object, where a “copy” is different than a clone, because with a copy you can change fields as desired during the copying process. The copy method is important in functional programming, where values (val) are immutable.

Yesterday I created a video tutorial on the Scala REPL and var & val variable types, and today I took a little time to create a new "Hello, world" Scala video tutorial. Without any further ado, here's the video:

If you're in the market for a Scala "Hello, world" tutorial, I hope you like it.

Here’s a nice 2009 article where Bill Venners interviews Martin Oderksy about the origins of Scala.

When you're using the SBT tool with your Scala projects, it can be helpful to list your "sbt history", the history of your SBT commands. Courtesy of the SBT tool itself, here are the history commands you can use from the sbt command line:

Scala is a great language in many ways. One great feature is that you can use it as a “Better Java” (i.e., as an OOP language), and you can also use it as a pure FP language. While some people prefer one extreme or the other (not unlike extremist Republicans and Democrats in the U.S.), I appreciate that this lets you find a “Middle Way” of using the best features of both approaches.

Because of personal reasons I have a fair amount of free time at the moment, so I started converting some algorithms in the book, Programming Collective Intelligence, from Python to Scala.

I just ran across this image in this presentation on ScalaCheck, and thought, “If you read my book, Learning Functional Programming in Scala, you know what that statement means.”

The next version of my book, Learning Functional Programming in Scala, is now available. See that link for details.

When you're working in the Scala REPL and want to see what methods are available on a class/object, you can create an instance of an object, follow that with the "." character, and then press the [Tab] key. This process, known as "tab completion" in the REPL, gives you a preliminary list of methods that can be called on the object.

Here's what this looks like when we try it on an Int object:

Update 1: The next version of my book on Scala and functional programming will be released later this week.

Update 2: The price of the book will be increased to $25 on July 1, 2017.

If you're looking for a simple Scala IMAP client tutorial/example, please follow that link, but if you're interested in some Scala source code that demonstrates IMAP searching with Scala, JavaMail, SearchTerm, AndTerm, FromStringTerm, SentDateTerm, FlagTerm, and FetchProfile, this source code may be for you.

In short, here's what the following Scala IMAP client does:

If you ever need to write an IMAP client in Scala, I hope the following example can be helpful. For my project named SARAH (a Mac OS X Siri-like project), I wanted an IMAP client to periodically check my mail and then say something a little better than, "You've got mail", and the first part of that was getting a Scala IMAP client going.

An functional programming idiom, and therefore a Scala idiom, is that functions and methods should not have side effects. As written in the book Programming in Scala:

A method's only act should be to compute and return a variable.

If you like old research papers, here’s a link to a 1999 article titled, A tutorial on the universality and expressiveness of ‘fold’.

The people at underscore.io have made their books on Scala and functional programming free (or “donationware,” if you prefer). I’ve found the Advanced Scala with Cats book to be particularly good, and well worth a donation.

(Full disclosure: I didn’t pay for the Advanced Scala book when I first downloaded it, then went back and tried to pay for it, but the Gumroad website wouldn’t let me do that.)

After the 0.1.2 release of Learning Functional Programming in Scala, it occurs to me that I need to be more explicit about my goals for the book. Some people seem to think that I’m trying to “sell” functional programming. That’s not the case at all. I’m just trying to be a reporter and explain what I’ve learned about FP after reading dozens (hundreds?!) of articles and many books on FP, learning Haskell, trying to apply these techniques to my own code, etc. I’ll explain this further in the next release of the book.

I haven’t watched all of this video yet, but it’s about how to build Scala projects with a tool named CBT.

Intellij IDEA has a reall nice help-tip hover tool that helps to explain some of Scala’s advanced language features. In this case the code Monad[M[_]] is a higher-kinded type, which I hope to explain more in my new book.

Problem: You want to add more unit tests and a main test suite to your ScalaTest tests.

Solution

To add more unit tests to your project, just create new test classes. For instance, to add a set of TDD-style tests for the Topping class, just create a ToppingTests class in the src/test/scala/com/acme/pizza directory:

If you've started using Scala, you've seen that there are some cool things in the Scala syntax compared to Java. For instance, in Java you'd execute a method on an object like this:

object.method();

But in Scala you definitely don't need the semi-colon:

object.method()

and then you can omit the parentheses: