Kotlin Flows - The Ultimate Guide
This article thoroughly covers a crucial concept in Kotlin Coroutines: Kotlin Flows. Flows are a reactive data structure you probably didn’t know, but you ca...
Posts by Year
2024
Functional Parallel Programming in the wild
A hands-on guide to speeding up the parallel processing power with the help of Scala & cats-effect fibers.
The Big Kotlin Tutorial
Learn Kotlin in the ultimate long-form, hands-on and comprehensive guide.
WebSockets in Http4s
Learn how to use WebSockets in Scala with Http4s, and how to enable two-way communication between the frontend and the backend.
Type Classes in Kotlin: A Practical Guide
Learn type classes in Kotlin - a powerful ‘design pattern’ to organize your code better and make it easier to read, understand and change.
How to Write a Full-Stack Scala 3 Application with the Typelevel Stack
Learn how to write a full-stack Scala 3 application with Cats Effect, Doobie, Http4s and Tyrian, from scratch.
2023
A guide to UDP in Scala with FS2
Understand how UDP works, and how you can transition from an old Java NIO implementation to a higher level API like FS2 in Scala.
Practical Type-Level Programming in Scala 3
Learn how to use type-level programming to solve practical problems.
A Functional Load Balancer with Scala, Http4s and Cats Effect
How to build an application load balancer with Scala & Cats Effect, featuring efficiency and concurrency. Tests included!
gRPC in Scala with Fs2 and Scalapb
A long-form guide on how to make microservices communicate with gRPC in Scala.
Functional Error Handling in Kotlin, Part 3: The Raise DSL
It’s time to end our journey on functional error handling in Kotlin with the new features introduced by the Arrow library in version 1.2.0. We’ll focus on th...
Scala as a Junior Developer
A story of a beginner developer learning and working with Scala.
REST APIs Using Play Framework and Scala: A Comprehensive Guide
Learn the basics of Play Framework to build robust HTTP APIs with Scala, in this long-form tutorial.
OAuth Authentication in Scala with Http4s
Learn how to implement OAuth authentication in Scala using Http4s, using GitHub as an OAuth provider.
Two-Factor Authentication in Scala with Http4s
Learn how to write a two-factor authentication mechanism using one-time passwords (HOTP and TOTP) with Scala and Http4s.
Kotlin Context Receivers: A Comprehensive Guide
This tutorial describes Kotlin context receivers, a new feature of the Kotlin language for nice and controllable abstractions.
Functional Error Handling in Kotlin, Part 2: Result and Either
In this article, we continue our journey through functional error handling by looking at the Result and Either data types and how to use them.
HTTP Authentication with Scala and Http4s
Learn how you can implement HTTP authentication with Scala and http4s, with 4 different methods: basic, digest, session and JWT tokens.
A Comprehensive Guide to Choosing the Best Scala Course
Discover the best Scala course for your learning journey. Explore the recommended courses and libraries like Cats Effect, ZIO, and Apache Spark.
Functional Error Handling in Kotlin, Part 1: Absent values, Nullables, Options
Whether we develop using an object-oriented or functional approach, we always have the problem of handling errors. Kotlin offers a lot of different methods t...
Configuring Http4s Security: CORS and CSRF
In this article, we will show you how to set up an Http4s server so that it correctly protects against cross-origin requests and CSRF.
The Ultimate Guide to Java Virtual Threads
Project Loom and virtual threads promise to bring modern concurrency paradigms that we already found in Kotlin (coroutines) and Scala (Cats Effect and ZIO fi...
From Akka Streams To Actors And Back
Interoperability between Akka Streams and actors with code examples
Streaming SQL with Apache Flink: A Gentle Introduction
A hands-on guide to Flink SQL for data streaming with familiar tools.
Optimizing Kafka Clients: A Hands-On Guide
Tips on how to make Kafka clients run blazing fast, with code examples.
Scala CLI Tutorial: Creating a CLI Sudoku Solver
Scala CLI is a great tool for prototyping and building Scala applications. We’ll use scala-cli, Scala Native and decline to build a brute-force sudoku solver.
Kotlin Coroutines - A Comprehensive Introduction
Kotlin coroutines are a powerful tool for asynchronous programming, and they fall under the umbrella of structured concurrency. Let’s check out their main fe...
2022
Finagle Tutorial: Twitter’s RPC Library for Scala
Finagle is a powerful and deceptively simple library for distributed systems, with built-in HTTP support, load balancing and more
Top 10 Skills (Mostly Mental Models) to Learn to Be a Scala Developer
Learning Scala doesn’t need to be hard. Here are 10 mental skills you can learn to be a good Scala developer.
A Backtracking Sudoku Solver in Scala
How to approach Sudoku and other constraint-satisfaction problems with recursive backtracking in Scala.
ZIO HTTP Tutorial: The REST of the Owl
How to set up an HTTP server with zio-http, the HTTP library in the ZIO ecosystem.
An introduction to SBT
Learn how to set up and configure your Scala projects with SBT in this long-form tutorial.
ZIO Streams: A Long-Form Introduction
A comprehensive introduction to ZIO streams, a powerful abstraction in the ZIO ecosystem.
Slick Tutorial
An introduction to the popular database library in Scala: Slick.
Stateful Streams with Apache Pulsar and Apache Flink
We discuss how you can integrate Apache Pulsar with Apache Flink to perform data enrichment with state from different topics.
Roadmap to a Successful Data Engineer
One of the most prominent Rock the JVM students shares his insights to a successful career in Data Engineering.
Scala Option: A Gentle Introduction
Scala Options are some of the first things we learn - but why? What do they do, and why are they useful?
Free Monad in Scala
A tutorial on the Free monad in Scala, how it works and what it’s good for.
Scala 3 and General Type Projections
Scala general type projections are unsound and were removed in Scala 3 - what do you mean?
Scala Generics: A Gentle Introduction
Scala generics are easy to understand if you come from a Java background. But what about Python or JS folks?
A Scala project with Akka, Cats and Cassandra
Akka, Cats and Cassandra in a bigger Scala project integrating multiple pieces in the Scala ecosystem.
Akka Typed: Actor Discovery
A common pattern in Akka Typed: how to find actors that are not explicitly passed around.
How to make a Snake game in Scala
The ultimate 10-minute tutorial to a Snake game in Scala.
FS2 Tutorial: More than Functional Streaming in Scala
The ultimate tutorial to purely functional streams in Scala with FS2.
Streaming Analytics with Apache Pulsar and Spark Structured Streaming
We’ll discuss the role Apache Pulsar plays in the event streaming and computing landscape, the use cases you can implement with Pulsar and when more advanced...
2021
A 2021 Retrospective
Wrapping up 2021 with an overview of what’s happened this year at Rock the JVM.
Learn Doobie for the Greater Good
We rely on the JDBC specification if we need to connect to SQL databases in the JVM ecosystem. However, JDBC is not a good fit if we use functional programmi...
Tagless Final in Scala
Demystifying the tagless final pattern in Scala. TLDR: it’s got nothing to do with type classes.
Evaluation Modes in Scala
We’ll take a look at some core Scala constructs and look at them from a different angle than we’re used to.
Akka Streams Backpressure
Akka Streams implements backpressure, a critical component of the Reactive Streams specification. This article is a demonstration of this mechanism.
Kafka Streams 101
Apache Kafka is clearly the leading technology concerning message brokers, and Kafka Streams brings a complete stateful streaming system based directly on to...
Type-Level Programming in Scala 3, Part 2: A Quicksort on Types
Level 90 of type-level programming: a real sorting algorithm on lists… as types.
Type-Level Programming in Scala 3, Part 1: Comparing Types
Learning how to use the power of givens to infer type relationships in Scala 3… at compile time.
Event Streaming with Apache Pulsar and Scala
Apache Pulsar is a cloud-native, distributed messaging and streaming platform that manages hundreds of billions of events per day. We’ll learn what makes it ...
Custom Pattern Matching in Scala
Pattern matching is one of Scala’s most powerful features. In this article, we’ll how to customize it and create our own patterns.
Another Take at Monads: A Way to Generalize Chained Computations
We’ve talked about monads quite a lot on Rock the JVM. In this article, we’ll approach them from yet another angle.
ZIO Kafka: A Practical Streaming Tutorial
Apache Kafka has proven itself as a reliable and scalable communication bus between distributed application components. We’ll learn to use ZIO to interact wi...
Why Should You Care About Referential Transparency?
Referential transparency is your best tool for productivity as a functional programmer in Scala. In this article, we’ll talk about what it is and why it’s im...
Exploiting Implicit Ambiguity in Scala
In this article, I’ll show you how you can exploit the implicit resolution mechanism in Scala to enforce type relationships at compile time.
Scala 3: Anti-Givens
Showing a Scala 3 trick that few developers know: exploiting the absence of a given instance to enforce type relationships.
ZIO: Introduction to Fibers
Many libraries implement the effect pattern in the Scala ecosystem, and every one has its own concurrency model. First, let’s introduce the ZIO library and i...
Unleashing the Power of HTTP Apis: The Http4s Library
Once we learned the basics of functional programming, it’s time to understand how to use them to expose APIs over an HTTP channel. If we know the Cats ecosys...
Cats: Essential Type Class Hierarchy, Explained
Cats is a complex library for Scala. In this article, we’ll deconstruct the major type classes of Cats and explain how they’re connected.
Scala Testing with ScalaTest: Test Styles for Beginners
In this article, we’ll go through the major testing styles with Scala and ScalaTest, and we’ll understand what ‘FunSuite’, ‘FlatSpec’ etc mean.
Scala Functional Collections
A short article with a powerful idea about functional collections many Scala programmers do not know about.
Cats Effect 3 - Racing IOs
After the previous introduction to concurrency in Cats Effect, we’ll look at how to manage racing IOs and fibers.
Cats Effect 3 - Introduction to Fibers
A quick dive into asynchronous computations with fibers in Cats Effect 3, written for Scala 3.
Scala 3: Extension Methods
Deconstructing extension methods, one of the most exciting features of the upcoming Scala 3.
Monads are Monoids in the Category of Endofunctors - Scala version, No Psychobabble
What’s the problem?
Scala 3: How Givens Can Work with Implicits
This quick article will show you how given instances in Scala 3 can work with Scala 2’s implicits.
Akka Typed: Adapting Messages
In this article we’ll see a good practice for organizing code, messages, domains and logic in an Akka application with Scala.
Semigroups and Monoids in Scala
This article is about Monoids and Semigroups as a gentle introduction to functional abstractions and to how the Cats library works.
N-Queens in Scala: How to Approach Algorithm Questions
Learn how to approach a Google-style algorithm interview question in Scala with pure functional programming.
Organizing Services with ZIO and ZLayers
ZIO layers (ZLayers) help us structure our complex services into modules that are independent, composable and easy to understand. Let’s take a look.
Value Classes in Scala
An ad-hoc type definition technique for eliminating bugs which are hard to trace, with implementations in Scala 2 via newtypes and in Scala 3 via opaque types.
Mutability in Scala
Although frowned upon by FP purists, creating and managing mutable data structures is important in any language. Scala has some first-class features.
Idiomatic Error Handling in Scala
Error handling is likely one of the most frustrating part of programming, and in Scala, there are better and worse ways to do it. Let’s take a look.
Match Types in Scala 3
Scala 3 comes with lots of new features. In this episode, match types: a pattern matching on types, and a tool for more accurate type checking.
How to Sort Lists in Scala with Tail Recursion
Sorting lists might be a “school” problem, but in this article I’ll show you how to use proper FP, tail recursion and more, using this popular example. Might...
Algebraic Data Types (ADT) in Scala
Every developer using Scala meets the acronym ADT sooner or later. In this article, we will try to answer all of your questions about ADTs.
Objects and Companions in Scala
This article is for the starting Scala programmer: an introduction to singleton objects and companions in Scala, what they can do, and why and where we shoul...
What the Functor?
In this article, we’ll explore one of the most used (and useful) concepts in pure functional programming: the Functor. Pretty abstract, so buckle up.
2020
2020 Retrospective (and What’s Coming in 2021)
In this article I’ll wrap 2020 and share a few insights, achievements and changes, and I’ll project some plans for the future of Rock the JVM.
Immutable Doubly Linked Lists in Scala with Call-By-Name and Lazy Values
I’ll show you a technique to use lazy values and call-by-name for recursive value definitions and implement a fully immutable doubly-linked list in Scala.
Scala 3: Path-Dependent Types, Type Projections, Dependent Methods and Functions
This quick tutorial will show you what dependent types are and how they work in Scala 3, along with dependent methods and functions.
Givens vs. Implicits in Scala 3
From the previous article, you know how givens work. Let’s compare them with the old Scala implicits.
Given and Using Clauses in Scala 3
The given/using clauses are some of the most important features of Scala 3. Read on for the essential concepts and how to use them.”
Variance Positions in Scala, Demystified
We’ll take a look at the famous “covariant type occurs in contravariant position” problem, and what we can do about it.
Let’s Talk About the Scala 3 Indentation
Some people love it, some hate it. Scala 3 indented syntax is not that bad, and it might actually help. Let’s take a look at how Scala 3 can change the struc...
Akka Typed: How the Pipe Pattern Prevents Anti-Patterns
Akka Typed has not only made fundamental changes in the actor protocol definitions, but made significant improvements in actor mechanics as well.
Akka Typed Actors: Stateful and Stateless
Akka Typed has fundamentally changed the way we create actors. In this article we’ll look at several ways we can keep state inside Akka actors.
ALL the Joins in Spark DataFrames
It’s obvious that Spark allows us to join tables. What’s not obvious is how many different kinds of joins Spark supports. We explore them in this article.
Broadcast Joins in Apache Spark: an Optimization Technique
Broadcast joins in Apache Spark are one of the most bang-for-the-buck techniques for optimizing speed and avoiding memory issues. Let’s take a look.
Type Lambdas in Scala 3
Exploring a quick but powerful structure in Scala 3 - type lambdas. This will help you think higher-level.
Types, Kinds and Type Constructors in Scala
Scala has a powerful type system. We look at how Scala types can be organized, what type constructors are, and why we should care.
Scala 3: Opaque Types
We discover opaque type aliases in Scala 3 and how we can define new types with zero overhead.
Scala 3 Traits: New Features
This article will continue some of the previous explorations of Scala 3. Here, we’ll discuss some of the new functionality of traits in Scala 3.
Enums in Scala 3
Scala 3 introduces enums. About time! Even though it might seem like something minor, it has important implications.
New Types in Scala 3
Scala 3 introduces some new kinds of types, which we’re eagerly awaiting for.
Lenses, Prisms and Optics in Scala
A really nice way to inspect, extract and modify deeply nested data structures in Scala.
Akka HTTP loves JSON: 3 Libraries You Can Integrate into Akka HTTP
Akka HTTP needs JSON like humans need water. We show you how to integrate Spray-Json, Circe and Jackson into Akka HTTP.
How to Deploy a Scala Application to AWS Lambda
Scala code is super easy to deploy to AWS lambda. We show you how in this step by step tutorial.
Refined Types in Scala
We look at how we can impose constraints on values at compile time with the Refined library.
Underscores are Overloaded in Scala!
Scala syntax is so confusing sometimes - I’ll show almost all uses of underscores in Scala. Sometimes the philosophy is inconsistent, but it’s worth at least...
Repartition vs Coalesce in Apache Spark
Drawing the line between two fundamental repartitioning operations in Apache Spark.
Eta-Expansion and Partially Applied Functions in Scala
We explore some not-so-well-understood territory in the form of eta-expansion and how methods and functions interoperate.
Type-Level Programming in Scala, Part 3
Final blow in the type-level trilogy. We learn how to sort lists… at compile time.
Type-Level Programming in Scala, Part 2
We continue down the path of type-level power in Scala. We learn to add numbers as types, at compile time.
Type-Level Programming in Scala, Part 1
This one is hardcode. We make the Scala compiler infer type relationships for us at compile time. Pure power.
The Practical Difference Between Abstract Classes and Traits in Scala
Abstract classes and traits share a lot of overlap in Scala. How are they actually different?
How Does “20 seconds” Work in Scala?
Various constructions like “20.seconds” look like baked into the Scala language. Let’s see how these work.
The Difference Between Null, Nothing, Nil, None and Unit in Scala
We explore the various flavors of nothing-ness in Scala.
How to Use Akka Streams Graph DSL
Akka Streams has the Graph DSL, which is one of its most powerful APIs. Learn how to use it and get started quickly with Akka Streams.
Comparing Akka Streams, Kafka Streams and Spark Streaming
We compare three of the most popular streaming libraries and see where Akka Streams, Kafka Streams and Spark Streaming are most useful.
Why are Type Classes Useful in Scala?
FP fans talk about pure functional programming in Scala with type classes. They’re hard. Why do we really need them?
Akka HTTP to Heroku in 10 Minutes
Akka HTTP is super easy to deploy to a web server. Learn how to use Heroku and deploy your first Akka HTTP service in minutes.
A Monads Approach for Beginners, in Scala
A Scala tutorial on Monads that makes no assumptions and starts from practical needs. We derive the monad patterns (“laws”) from scratch.
5 Nice Scala Tricks for Expressiveness
Scala is an amazingly expressive language, but even the most experienced devs aren’t aware of all the subtleties.
How to Create Your Own Custom String Interpolator
Yep, you can write your own interpolator that looks like it was built into the Scala language. Learn how.
How Akka Typed Incentivizes You to Write Good Code
Akka Typed is one of the best things that happened with the Akka API. We explore how good practices are baked into the API directly.
Sync, Async and (non) blocking in Scala and Akka
We discuss the tradeoffs between 3 different styles of writing parallel code, in terms of thread use (and other effects) in Scala and Akka.
4 Nice Ways to Read Files in Scala
Learn to read files in Scala like a boss and compare it to other styles in other languages. We write a simple API which looks almost as easy as Python’s read...
3 Fun Tricks with Call-By-Name in Scala
Maximize the call-by-name semantics in Scala and manipulate your results when you want them.
Reading Spark DAGs
We walk you through one of the foundational skills for Spark performance optimization: reading the Spark UI and the graph of how your job is structured.
Much Ado About Nothing in Scala
We go on a short trip to Nothing (and nothing-ness) in Scala. Nothing is actually pretty useful.
How Things Don’t Make Sense - Scala Loops
Daniel goes into another rant about learning (and teaching) Scala using loops. Are they actually useful?
Materialized Values in Akka Streams
We demystify one of the hardest concepts in Akka Streams: materialized values.
Reading Spark Query Plans
In this article you’ll learn one of the most important Spark skill: reading how your job will run. This is foundational to any further Spark optimization.
How Things Don’t Make Sense - Scala Variables
Daniel goes into a small rant about learning (and teaching) Scala using variables.
Higher-Order Functions for OO Programmers
For OO programmers looking to dive into functional programming in Scala: a gentle introduction to functions working with other functions.
Controllable Futures in Scala
In this article we learn to address the problem of “deterministic” Futures in Scala, using Promises.
Self-types in Scala, Real Quick
Self types are a really interesting way to enforce type constraints in Scala. Learn to use it in a few minutes.
Sending HTTP Requests in Scala and Akka in 5 minutes
Learn to use Akka HTTP with Scala and send HTTP requests in just a few minutes with the Akka HTTP server DSL.
Why is Scala contravariance so hard?
The Scala type system is powerful, but also hard. We look at contravariance in Scala and try to make some sense out of it.
8 Scala Pattern Matching Tricks
Pattern matching is one of the most powerful Scala features. Learn to use it to the max so you can write your best Scala code.