Scala, Java, Unix, MacOS tutorials (page 3)

(Note: This is one of over 1,000 lucid dreams that I have had and made notes about. For some reason I have had lucid dreams (and sleep paralysis) quite often, so at some point I started making notes about the dreams.)

I fell asleep very slowly last night, so I was able to stay awake through the whole falling-asleep process, i.e., the usual sleep paralysis part. As I was still awake I started to hear the usual “here/there sucking sounds,” and just told myself that I shouldn’t be afraid, I’ve done this hundreds of times before.

And then the instant I fell asleep here I found myself in a hospital there. A doctor and nurse were looking at a bandage on the lower-right part of my abdomen, above the appendix, and closer to the center of the stomach.

As I looked at “myself,” I noted that the skin color was lighter than mine, and that my arms were smaller and skinnier, and there wasn’t much hair on the abdomen or arms. After the inspection the doctor asked if I had any questions, and I said, “Yes. Who am I? And where am I?”

I’ve probably documented over 1,000 lucid dreams in the last 20 years or so, and here’s another one from this morning. To me, the most important part about this one is the hypnopompic hallucination stuff I note at the end.

Had a long dream — approximately 2:30-4am — about “my wife” doing drugs without me knowing it.

I starts with us driving in a seedy part of town. She had mentioned that she knew someone who could get us some drugs if I/we wanted to try them. We ended up getting something that looked like a small rock or stone.

I’ve been slowly working on a series of new Scala programming books, and today I’m proud to announce the first of these:

Starting today you can buy the PDF version of Learn Scala 3 The Fast Way! for just ten dollars — $10 (USD) — at this Gumroad.com URL.

MARCH, 2023: This book was previously named Learn Functional Programming Without Fear, but I have renamed it to Learn Functional Programming The Fast Way. I think this name is more reflective of the ZIO and Cats Effect libraries being easier to learn than ever before (without having to know category theory), and the name is also consistent with my other book, Learn Scala 3 The Fast Way.

NOV., 2022: My new book, Learn Functional Programming Without Fear, is currently an Amazon Java and functional programming #1 new release. The book is now available in three formats:

Scala FAQ: How can I use the startsWith method on a Scala String to match multiple possible patterns in a match expression?

Solution

As shown in the following example, you can use the startsWith method on a String to match multiple possible patterns in a match expression. startsWith checks to see if a String starts with the prefix (or substring) you specify, so although in these examples I use complete strings, you can also use regular expression patterns.

Example: startsWith + match expression

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:

Scala FAQ: What is the Nothing type in Scala, and how do I use it?

Solution

In Scala, the Nothing type is called a bottom type, which means it is a sub-type of every other type in the Scala type system. It is also specifically a data type that has no instances.

In practical use, Nothing is used to indicate that a computation or function will never produce a result normally, either because it throws an exception, enters an infinite loop, or encounters some other abnormal termination.

Visually, this is what the Nothing type looks like in the Scala type hierarchy (image courtesy of this scala-lang.org page):

Scala: Common uses of Nothing

Some common use cases of Nothing in Scala include: