When building a software project with a given scope there are three main constraints you can trade off: good, fast, and cheap. This is commonly known as the project management triangle. Focusing on one will have an effect on the others. For example, trying to do things cheap will adversely affect good and fast.

People new to functional languages often struggle a bit with the concept of recursion, and in particular tail recursion. In this post we’ll look at both recursive and tail recursive functions using the substitution model to show their effect on the stack. We’ll also walk through deriving fold, map, and other functions from first principles because it fairly naturally follows on from this.

Validation is something that every API developer has to deal with, but causes a surprising amount of confusion. Should the validation be done in the controller, the model, or a service class? Is the value of an attribute being invalid part of the request validation or business logic validation? By changing the way we think about validation the answers to these questions drop out, along with a nice implementation for Akka HTTP.

When I looked through some of Deliveroo’s non-Ruby applications, I saw that a number of them were trying to copy the ActiveRecord approach and defining data access methods on the models themselves. This is not a good approach in statically typed languages. I’ll explain why, and demonstrate the approach you should be using. It’s no secret that I’m not a fan of Go, but I’ll use it here to demonstrate as the majority of the applications I’ve seen with this problem are written in it.

People coming from dynamic languages like Ruby or primitive languages like Go tend to miss the point of Scala. They tend to think in terms of mutability and often aren’t familiar with data structures beyond lists and hashes, with types and side effects being seen as fairly unimportant considerations. To try and illustrate the different way you need to think when writing Scala I’m going to write a ring buffer, as I’ve seen a few people around the office implementing them as a learning exercise.