Boolean Is Not Your Friend

Many programmers accept using Boolean values in domain modeling. That is an old habit, and the bad one. It only takes a few lines of code to demonstrate its destructive effects.
Still, there is a cure for that problem. Its application is straightforward for anyone who wishes to see the root cause of this class of modeling issues.

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👨 About Me 👨
Hi, I’m Zoran, I have more than 20 years of experience as a software developer, architect, team lead, and more. I have been programming in C# since its inception in the early 2000s. Since 2017 I have started publishing professional video courses at Pluralsight and Udemy and by this point, there are over 100 hours of the highest-quality videos you can watch on those platforms. On my YouTube channel, you can find shorter video forms focused on clarifying practical issues in coding, design, and architecture of .NET applications.❤️
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[plgueis]

Best video to date. Loved how it clearly showed step by step how a code base degregates with "just one more change request" and how to propertly fix it. I hate these flag bools with a passion.

[cj-hy]

The boolean is not my friend? Well, in all fairness, it's "a bit on again, off again"

[TPInspector]

Basically, if you have a class with an attribute that represents multiple states, you can use subclasses to represent each of these states. This approach makes the code cleaner and more organized. It also makes it easier to handle changes, which is important because clients often have additional requirements or changes in the future. Thanks Zoran

[nickbarton]

How I giggled at the first law of customer requirements, that they never stop.
The second law is like unto it, they want it yesterday.
Great job Zoran.

[neeeeeck]

This is what differentiates good programmers, if programmer doesn't understand or doesn't want to understand a hollistic picture of the product and requirements they're developing, they would not come up with this solution. This solution shows understanding of not just programming, but analysis and thorough understanding off business logic. Always understand what you are coding, and why you are coding it, before you start coding it.

[drg]

Marvellous video. As an F# user, I've been drifting away from using explicit class inheritance, but it's very inspiring to see it well done. Starting with a bad design is a great plot device.

[fswerneck]

Definitely the right way of writing code.

I was butting heads these days exactly because of this at work. Coworkers who are closer to management got to include code with potentially invalid states in it, and a boolean. Like: thing.is_partnership: bool, str | null, and thing.partnership_enddate: datetime | null. During code review I pointed how the boolean is unnecessary, and that it would be better for those fields to be tightly coupled into a new type, Partnership, that could itself be nullable in this context, as in, thing.partnership: Partnership | null. If it's null, there's no partnership. If it isn't, then for certain there will be a description and an end date. They ignored my comments and merged anyway.

[batek]

I really can't follow a single video, it starts in the middle of an already started project, the narration is abstract and poem-like, the explanation is confusing and all over the place. He seems like a good developer, not a good teacher, the whole point of the video was if you have a class with an attribute that represents multiple states, you can use subclasses to represent each of these states, and i got that from a comment, HE never said that, he was all like "In the realm where code does weave,
A tale of logic, pure and brief,
There lies a class, a single form,
With attributes that should transform". Personally I think Milan Jovanovic is the best .net online teacher at the moment, him and Mohamad Lawand.

[NullzeRT]

First thing I thought of is a Rust's enum, which is algebraic type, meaning that each of it's variants can contain it's own data. And it turned out was the correct answer with analogous construction in C#. In Rust this solution comes to mind sooner, since its a very common practice and one of the core features of the language.

[Gremirz]

This OOP approach is just beautiful. You good sir just sold me your course.

[yimyim]

Good demonstration of using inheritance to abstract away binary states. Although a data driven design approach would also yield high simplification. Why store the information of being published at all? You can manage these states as containers, e.g. a list of published books, a list of unpublished ones etc. But of course it depends on the context.

[StefanH]

An even slightly flawed model can have massive implications and introduce pain points. Great showcase of how data models should be designed to make invalid statd impossible to represent

[mkwpaul]

Great video, superbly explained and illustrated.
I just wanna point out that this isn't just good practice when doing ddd or OO but any programming style be it functional, purely imperative, data-oriented, or in this case DDD/OO.

Properly modeling your data, and making invalid states unrepresentable on the type level, is the biggest lesson to learn here.
And this modeling generally requires much more fine-grained types than many developers are used to.

The "IsPublishedBefore" check is implemented here as a virtual method on the base type, but could just as easily be a static extension method with a swtich expression instead in a functional or imperative data-oriented style.
Of course there are always exceptions, where booleans are truly domain >data< and not a misguided way of implementing a more complex piece of information.

[chlojolo]

I am grateful that the next time I have to explain to someone that bool is not their friend, I will now have the option to send this video. With any luck, they may even heed it.

[markky]

Please don't stop your mission Ser!

[tryoxiss]

I know this is an example in Java (OH, its C#, they are so simillar I missed it), so this solution wont work here, but if you are using a language with sum types (Rust, functional-programming), you can use an enum:

enum {
Published(Date),
Scheduled(Date),
Unpublished
}

[roll-outcommanders]

I find your videos tantalizing, provocative and very informative. Although I have come to the end of my software engineering career ("career" use as verb here) I am sure I will still take interest in what you have to say although I will never get to engineer any of your insights. Thank you Zoran and keep up the good work.

[baranacikgoz]

That's why I think one must master the strategy pattern before write code. Excellent video.

[juliogomez]

You are a true genius of clean design! I've learned a lot with this video and I am excited to continue learning stuff with your videos. Thanks for sharing your knowledge with the world!

[josebarria]

Good video.
Note that this applies not only to domain models.but also to game design.. instead of representing states with a bool, just take the time to make it more complete