collections

Think of the Scala collections’ map method as “transform”

I’ve written this before, but when I saw this “pseudocode to Scala code” example in the book Functional Thinking, I thought it was worth mentioning again: If you have trouble grokking the Scala map method, think of it as being named transform instead. It transforms an input collection to an output collection, based on the algorithm you supply.

For those coming from the OOP world, I think “transform” is a better word because it is more meaningful, at least initially.

Kotlin collections methods: examples and syntax

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")

Scala 2.13.0-M4 release notes (collections changes)

Under the covers — and sometimes above the covers — Scala is changing. These notes about Scala 2.13.0-M4 describe some of the changes coming to the Scala collections classes.

A few things not shown in the image are:

  • The scala-xml library is no longer bundled with the release
  • Procedure syntax (def m() { ... }) is deprecated
  • View bound syntax (A <% B) is deprecated
  • Assorted deprecated methods and classes have been removed

See the Scala 2.13.0-M4 release notes for more details.

An Illustrated Guide to Covariance and Contravariance

From the article I linked to: “Generics can often seem confusing. How often have you started to solve a problem with generics, only to realize that they don’t quite work like you thought they did? The good news is that there are some simple, foundational concepts that underpin generic variance. And once you understand those concepts, you won’t have to memorize acronyms or resort to trial-and-error - you’ll simply understand how and why they work.”

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.