Get this book on Leanpub

A couple of weeks ago, Tomas Votruba emailed me saying that he just realized that we hadn’t published an update of the book we wrote together since December 2021. The book I’m talking about is “Rector - The Power of Automated Refactoring”. Two years have passed since we published the current version. Of course, we’re all very busy, but no time for excuses - this is a book about keeping projects up-to-date with almost no effort… We are meant to set an example here!

Refactoring without tests should be fine. Why is it not? When could it be safe?

From the cover of “Refactoring” by Martin Fowler:

Refactoring is a controlled technique for improving the design of an existing code base. Its essence is applying a series of small behavior-preserving transformations, each of which “too small to be worth doing”. However the cumulative effect of each of these transformations is quite significant.

Software development seems to be about change: the business changes and we need to reflect those changes, so the requirements or specifications change, frameworks and libraries change, so we have to change our integrations with them, etc. Changing the code base accordingly is often quite painful, because we made it resistant to change in many ways.

Code that resists change

I find that not every developer notices the “pain level” of a change. As an example, I consider it very painful if I can’t rename a class, or change its namespace. One reason could be that some classes aren’t auto-loaded with Composer, but are still manually loaded with require statements. Another reason could be that the framework expects the class to have a certain name, be in a certain namespace, and so on. This may be something you personally don’t consider painful, since you can avert the pain by simply not considering to rename or move classes.

TLDR;

Rector - The Power of Automated Refactoring is now 100% completed

Tomas Votruba and I first met a couple of years ago at one of my favorite conferences; the Dutch PHP Conference in Amsterdam (so actually, we’re very close to our anniversary, Tomas!). He presented Rector there and it was really inspiring. A year later I was working on a legacy migration problem: our team wanted to migrate from Doctrine ORM to “ORM-less”, with handwritten mapping code, etc. I first tried Laminas Code, a code generation tool, but it lacked many features, and also the precision that I needed. Suddenly I recalled Rector, and decided to give it a try. After some experimenting, everything worked and I learned that this tool really is amazingly powerful!

In October 2020 I asked Tomáš Votruba, the mastermind behind Rector, if we could have a little chat about this tool. I wanted to learn more about it and had spent a couple of days experimenting with it. Tomáš answered all my questions, which was tremendously valuable to me personally. When this happens I normally feel the need to share: there should be some kind of artefact that can be published, so others can also learn about Rector and how to extend it based on your own refactoring needs.

You’ve picked a good refactoring goal. You are prepared to stop the project at anytime. Now how to determine the steps that lead to the goal?

Bottom-up development

There is an interesting similarity between refactoring projects, and regular projects, where the goal is to add some new feature to the application. When working on a feature, I’m always happy to jump right in and think about what value objects, entities, controllers, etc. I need to build. Once I’ve written all that code and I’m ready to connect the dots, I often realize that I have created building blocks that I don’t even need, or that don’t offer a convenient API. This is the downside of what’s commonly called “bottom-up development”. Starting to build the low-level stuff, you can’t be certain if you’re contributing to the higher-level goal you have in mind.

Refactoring is often mentioned in the context of working with legacy code. Maybe you like to define legacy code as code without tests, or code you don’t understand, or even as code you didn’t write. Very often, legacy code is code you just don’t like, whether you wrote it, or someone else did. Since the code was written the team has introduced new and better ways of doing things. Unfortunately, half of the code base still uses the old and deprecated way…

Refactoring projects

A common case of refactoring-gone-wrong is when refactoring becomes a large project in a branch that can never be merged because the refactoring project is never completed. The refactoring project is considered a separate project, and soon starts to feel like “The Big Rewrite That Always Fails” from programming literature.

The work happens in a branch because people actually fear the change. They want to see it before they believe it, and review every single part of it before it can be merged. This process may take months. Meanwhile, other developers keep making changes to the main branch, so merging the refactoring branch is going to be a very tedious, if not dangerous thing to do. A task that, on its own, can cause the failure of the refactoring project itself.

In the first and second part of this series we’ve been doing quite a bit of work to separate concerns that were once all combined into one function.

The major “players” in the field have been identified: there is an HttpClient and a Cache, used by different implementations of CatApi to form a testable, performing client of The Cat Api.

Representing data

We have been looking at behavior, and the overall structure of the code. But we didn’t yet look at the data that is being passed around. Currently everything is a string, including the return value of CatApi::getRandomImage(). When calling the method on an instance we are “guaranteed” to retrieve a string. I say “guaranteed” since PHP would allow anything to be returned, an object, a resource, an array, etc. Though in the case of RealCatApi::getRandomImage() we can be sure that it is a string, because we explicitly cast the return value to a string, we can’t be sure it will be useful to the caller of this function. It might be an empty string, or a string that doesn’t contain a URL, like 'I am not a URL'.

The world is not a safe thing to depend upon

When you’re running unit tests, you don’t want the world itself to be involved. Executing actual database queries, making actual HTTP requests, writing actual files, none of this is desirable: it will make your tests very slow as well as unpredictable. If the server you’re sending requests to is down, or responds in unexpected ways, your unit test will fail for the wrong reasons. A unit test should only fail if your code doesn’t do what it’s supposed to do.

Some time ago I tweeted this:

I didn't mention this yet, but I'm working on a series of videos about the subject matter of my Principles of Package Design book.

— Matthias Noback (@matthiasnoback) May 14, 2015

It turned out, creating a video tutorial isn’t working well for me. I really like writing, and speaking in public, but I’m not very happy about recording videos. I almost never watch videos myself as well, so… the video tutorial I was talking about won’t be there. Sorry!