Scala: How to use higher-order functions with Option (instead of match expressions)
Table of Contents
I originally wrote a long introduction to this article about Scala Options, but I decided to keep that introduction for a future second article in this series. For this article I’ll just say:
- idiomatic Scala code involves never using null values
- because you never use nulls, it’s important for you to become an expert at using
Option,Some, andNone - initially you may want to use match expressions to handle
Optionvalues - as you become more proficient with Scala and Options, you’ll find that match expressions tend to be verbose
- becoming proficient with higher-order functions (HOFs) like
map,filter,fold, and many others are the cure for that verbosity
A good reason to use sealed traits and classes in Scala
This scala-lang.org documentation page shares a good reason to use “sealed” traits and classes: When you created sealed traits, the compiler can easily tell all of the subtypes of your class or trait, and as just one benefit, you don’t need to add a default, “catch-all” case in your Scala match expressions.
Scala: How to use regex pattern matching in a match expression
Scala FAQ: How can I use regular expression (regex) pattern matching in a match expression (a Scala match/case expression)?
As I wrote in my Scala sed class post earlier today, Jon Pretty’s Kaleidoscope project lets you use string pattern-matching code in Scala match expressions. This enables regex pattern-matching code like this:
A little Scala `sed` class
A few times during the past year I got tired of trying to remember the Unix/Linux sed syntax while wanting to make edits to many files, so this weekend I wrote a little sed-like Scala class.
Scala: How to use fold on an Option (syntax)
Scala/Java: How to write a pattern that matches a minimum to maximum number of specified characters
If you’re using Java or Scala and need to write a pattern that matches a range of characters, where those characters occur between a minimum and maximum number of times in the pattern, the following example shows a solution I’m currently using.
The idea is that the pattern "[a-zA-Z0-9]{1,4}" means, “Match a string that has only the characters a-z, A-Z, and 0-9, where those characters occur a minimum of one time and a maximum of four times.” The following tests in the Scala REPL shows how this works:
A Scala shell script to insert text before a matching pattern
I don’t remember exactly why I wrote this Scala shell script, but if I remember right I was having a problem getting sed to work properly, so I wrote this little script to insert an Amazon Kindle “break” tag before each <h1> tag in an HTML file:
As a brief note about the Linux/Unix sed command, today I learned how to append multiple lines of text to an HTML (or XML) file on macOS. The short answer is that I created a sed commands file named changes.sed with these contents:
Scala: How to extract parts of a String that match regex patterns
This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 1.9, “Extracting Parts of a String that Match Patterns.”
Problem
You want to extract one or more parts of a Scala String that match the regular-expression patterns you specify.
Solution
Define the regular-expression (regex) patterns you want to extract, placing parentheses around them so you can extract them as “regular-expression groups.” First, define the desired pattern:
How to find regex patterns in Scala strings
This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 1.7, “Finding Patterns in Scala Strings.”
Problem
You need to determine whether a Scala String contains a regular expression pattern.