foreach

Scala: How to use higher-order functions with Option (instead of match expressions)

Table of Contents1 - Sample data2 - From match expressions to higher-order functions3 - Notes4 - Resources5 - Comments

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, and None
  • initially you may want to use match expressions to handle Option values
  • 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
Kotlin collections methods: examples and syntax alvin November 14, 2018 - 10:23am

As a quick note today, if you ever need some examples of how the Kotlin collections methods work, I hope these examples are helpful.

Sample data

First, here’s some sample data:

val a = listOf(10, 20, 30, 40, 10)
val names = listOf("joel", "ed", "chris", "maurice")

The Kotlin forEach println syntax

It’s a little hard to move back and forth between Scala and Kotlin because of some of the differences between the languages. Skipping the long story, here’s an example of how to print every line in a list of strings in Kotlin using forEach and println. First the setup:

import java.io.File
fun readFile(filename: String): List<String> = File(filename).readLines()
val lines = readFile("/etc/passwd")

Then here are two different ways to use forEach with println:

Methods on the Scala collections classes, organized by category

When I wrote the Scala Cookbook, I gave each recipe and then each chapter my full attention. I thought that if I wrote each recipe as well as possible, and included important recipes in each chapter, well, I wanted each chapter to be worth the price of the entire book. That was my goal.

As a result of this effort -- and perhaps to the chagrin of my editor -- the Scala collections chapters ended up being 130 pages in length.

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.

This is a page from my book, Functional Programming, Simplified

How to Enable the Use of Multiple Generators in a ‘for’ Expression

One cool thing about for expressions is that you can use multiple generators inside of them. This lets you do some nice analytics when you have some interesting data relationships.

For instance, suppose you have some data like this:

This is a page from my book, Functional Programming, Simplified

How to Enable Filtering in a Scala `for` Expression

Next, let’s see if we can use a filtering clause inside of a for expression with the Sequence code we have so far.

Trying to use a filtering expression

When I paste the current Sequence class and this code into the Scala REPL:

val ints = Sequence(1,2,3,4,5)

val res = for {
    i <- ints
    if i > 2
} yield i*2

I see the following error message: