Onion Architecture: An Unstable Equilibrium

The Onion architecture (Figure 1) is a well-known architectural pattern, although we often call it something else: Hexagonal architecture, Ports and Adapters, Clean architecture. The goal of all these patterns is the same: Decoupled layers and a clear separation of concerns. With that in place,...

Functional Mars Rover kata: Railways on Mars

In the previous article, we discussed and implemented domain types for the Mars Rover kata. Now, we will go through the rest of the requirements and implement the command execution functionality. First, we need to parse an input sequence of characters in order to determine which movement functions...

Functional Mars Rover kata: Domain modeling

In the following article series, we are going to explore a functional approach to the Mars Rover kata. It is a well-known kata and you can find a lot of different solutions implemented in object-oriented programming languages like Java or C#. We are going to use F# for our implementation. Even if F# is a multi-paradigm programming language, the goal is to implement the kata in a purely functional...

A software developer as a software user

In the first few years of my career, I had an opportunity to work on projects which included mechanical design. I studied mechatronics, so besides writing software, I was also involved in the design of mechanical components until later on, when I completely shifted my focus on programming and software...

Messaging - the essence of OOP

Note: This article is highly influenced by the work of Sandi Metz. Her books and lectures helped to fill in the missing pieces in my current understanding of the object-oriented design. Probably we all heard about following job interview question: "What are the four pillars of object-oriented programming?" The...

"Mockist" or "Classicist"? Both!

From time to time, an article or a talk with an interesting name pops up on the internet: TDD is dead, Mocking sucks, Object-oriented programming is embarrassing, ... In my opinion, these kinds of articles are good for the industry because it encourages discussion and inspires us to re-examine our views. However, one of the things that is common for most of these articles and talks is a placement...