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Comment by starlust2 | Hacker News Reader

> Maybe in the not-too-distant future we will have AI grokking large code bases and cranking out accurate, useful, UML diagrams out of it.

> All those diagrams, when they are complete, correct and up-to-date, do convey what they are supposed to convey.

I spent a bit of time prototyping this recently. It's definitely possible. Rational Rose also had the capability to generate diagrams from code though. I don't remember how good it was at the task though. Was Rational Rose just a very bad implementation?

I find the hate in this chat strange because diagrams are incredibly useful when working through complex problems* and then conveying that information to other engineers. My experience over 20+ years is that a huge portion of engineers can't grok complex problems from code alone.

*Most of my projects are optimizing billion+ row databases, micro-service architectures, and various other scaling challenges.

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The problem isn't generating UML from code, the problem is generating useful UML from code.

Where those boxes are in relation to each other matters. You can't just randomly throw boxes and lines on the page, you need to arrange them so that boxes that we can tell what things are related by how close they are to each other. Automatic UML doesn't capture that.

Sometime you have complexity in code that needs tobe hidden by default. I don't care about rare error cases most of the time, but automatic UML can't know what is the complexity needed for rare cases and what is complexity you need to show the junior on the first day.. related to this when i'm interested in one error path how do you hide the others?

Then the real killer of both. Next week there is a minor requirement change (new features we always knew were coming and planned for even), and now the code changed. UML doesn't follow that. Either you generate UML and have the above problems. Or you manually update UML in theory, but in practice just let it slide as the week after you know something else will change and you don't nees it today anyway.

> Or you manually update UML in theory, but in practice just let it slide as the week after you know something else will change and you don't nees it today anyway.

I've heard this argument many times, but how is it different from keeping documentation, comments, tests, or the issue tracker up to date?

They all require some discipline, but if the team finds value in any of these things, they would make an effort to keep them synchronized with the code.

Besides, I suggest not falling in the trap of having formal design documents early on in the project's lifetime. Rather start with informal diagrams and sketches, and once the design has mostly settled, switch to something like UML. This would mean it wouldn't require changes every other week.

As for automatically generating, and dynamically arranging diagrams, this is more up to the generating tool than UML. These tools are still stuck using decades old technology at this point AFAIA, but there's no reason that a smarter tool couldn't do the things you mention.

> The problem isn't generating UML from code, the problem is generating useful UML from code.

I would kill for a tool that could output class and sequence diagrams from a project or component. If the format is editable and tools can automatically layout/filter out components, all the better. Right now the main time sink in putting together diagrams is trying to express what's in the code. Once that's in place, we can prune stuff we don't need.

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