This article shows an example of framework decoupling. You’ll find a more elaborate discussion in my latest book, Recipes for Decoupling.

Why would it be nice to decouple your user model from the framework’s security user or authentication model?

Reason 1: Hexagonal architecture

I like to use hexagonal architecture in my applications, which means among other things that the entities from my domain model stay behind a port. They are never exposed to, for instance, a controller, or a template. Whenever I want to show anything to the user, I create a dedicated view model for it.

My new book Recipes for Decoupling is 100% complete and available now!

And now some other news related to this book.

A little background information

My new book is based on two things: 20 years of experience with (mostly framework) coupling issues in legacy code, and the hypothesis that PHPStan, the automated static analysis tool for PHP, can help us keep our code decoupled. Decoupling often means we want to use a dependency, but don’t want to couple our code too tightly to it. The process of decoupling often involves some kind of rule, like “don’t use Container::get()”, but we don’t want to focus on this rule all the time, or explain it to new members of the team. Instead, we want a tool that shows you an error when you don’t follow the rule. Such an error will break the build of the project and prevent you from ever coupling to a dependency in this specific way again.

Years ago my co-worker Maurits introduced me to the term “magic” in programming. He also provided the valuable dichotomy of convention and configuration (or in fact, he’d choose configuration over convention…). I think this distinction could be very helpful in psychological research, figuring out why some people prefer framework X over framework Y. One requires the developer to spell out everything they want in elaborate configuration files, the other relies on convention: placing certain files with certain names and certain methods in certain places will make everything work “magically”.

This article is an excerpt from my book Advanced Web Application Architecture. It contains a couple of sections from the conclusion of Part I: Decoupling from infrastructure.

This chapter covers:

• A deeper discussion on the distinction between core and infrastructure code
• A summary of the strategy for pushing infrastructure to the sides
• A recommendation for using a domain- and test-first approach to software development
• A closer look at the concept of “pure” object-oriented programming

Core code and infrastructure code

In Chapter 1 we’ve looked at definitions for the terms core code and infrastructure code. What I personally find useful about these definitions is that you can look at a piece of code and find out if the definitions apply to it. You can then decide if it’s either core or infrastructure code. But there are other ways of applying these terms to software. One way is to consider the bigger picture of the application and its interactions with actors. You’ll find the term actor in books about user stories and use cases by authors like Ivar Jacobson and Alistair Cockburn, who make a distinction between:

As a rather unusual pastime for the Saturday night I attended the third Domain-Driven Design Africa online meetup. Thomas Pierrain a.k.a. use case driven spoke about his adaptation of Hexagonal architecture. “It’s not by the book,” as he said, but it solves a lot of the issues he encountered over the years. I’ll try to summarize his approach here, but I recommend watching the full talk as well.

Hexagonal architecture

Hexagonal architecture makes a distinction between the use cases of an application, and how they are connected to their surrounding infrastructure. Domain logic is represented by pure code (in the FP sense of the word), surrounded by a set of adapters that expose the use cases of the application to actual users and connect the application to databases, messages queues, and so on.

Since I’ve been writing a lot about decoupled application development it made sense that one of my readers asked the following question: “Why should we use a framework?” The quick answer is: because you need it. A summary of the reasons:

• It would be too much work to replace all the work that the framework does for you with code written by yourself. Software development is too costly for this.
• Framework maintainers have fixed many issues before you even encountered them. They have done everything to make the code secure, and when a new security issue pops up, they fix it so you can just pull the latest version of the framework.
• By not using a framework you will be decoupled from Symfony, Laravel, etc. but you will be coupled to Your Own Framework, which is a bigger problem since you’re the maintainer and it’s likely that you won’t actually maintain it (in my experience, this is what often happens to projects that use their own home-grown framework).

So, yes, you/we need a framework. At the same time you may want to write framework-decoupled code whenever possible.

Decoupling from a service locator - shouldn’t that be: don’t use a service locator?

Well, not really, since there are lots of valid use cases for using a service locator. The main use case is for making things lazy-loading (yes, you can also use some kind of proxy mechanism for that, but let’s assume you need something simpler). Say we have this EventDispatcher class:

class EventDispatcher
{
    public function __construct(array $listeners)
    {
        $this->listeners = $listeners;
    }

    public function dispatch($event)
    {
        foreach ($this->listeners[$event] as $listener) {
            $listener->notify();
        }
    }
}

Now it appears that some event listeners are rather expensive to instantiate. And, even though it may never be notified (because it listens to a rare event), in order to register any event listener, we need to instantiate it: