I don't think I have ever seen anybody actually getting value from a class diagram. I have seen many people creating them, but they are always useless.

I also don't think the UML variant of state machines and workflow are any popular. But well, there is probably somewhere where people use them. Also, those lists usually ignore entity-relationship diagrams, where UML just adopted the popular format (without even minor changes, like for workflows), and thus everybody uses the UML one.

But yes, people don't remember about deployment diagrams. Those are used a lot.

> I have seen many people creating them, but they are always useless.

Not every artifact is worth keeping, instead the value can come from the process of creation as a way to structure your thoughts or to explain or brainstorm possible solution. The value of class diagrams for those people is in the moment and it’s ok to throw them away later if they become useless.

Class diagrams are a good way to detect circular dependencies.

If your class diagram is comprehensive enough to get circular dependencies, then I'm completely sure¹ nobody will use them for anything.

Computers are much better at this kind of checks anyway, and they don't need diagrams.

1 - Instead of "well, maybe it's possible despite I never seeing it"

> I think it mostly depends on maturity of the team and engineering culture, whether UML is used or not.

I suspect that's true: teams with a very immature engineering culture probably do use a lot more UML. It's a good way to feel like you're doing something useful instead of actually doing the hard part. Mature teams write code.

Part of engineering culture in general, not just software engineering, is ability to share knowledge though documentation and best practices. If you share the source code, you communicate your solution on a very low level. It is often necessary to zoom out to see the big picture and there visualization helps. You can create ad-hoc diagrams, but their expressive power is low: without a convention it’s basically just space, text, arrows and generic shapes. To increase the expressive power you need a visual language in which different shapes and lines have some semantics. And here comes UML and other diagram languages. If you are not using them, it is likely that you are not communicating efficiently. Can a mature team fail at communication? I leave the answer to you.

UML didn't help though because it is never kept up to date with what the code really is

How was it supposed to keep up? The most popular programming languages did not introduce concepts that are too hard to reflect with UML. Or do you mean the problem of maintaining documentation?

Maintaining documentation. UML cannot go even one developer-week without being updated, but the developer will often not do that. By the time your UML is a month out of date it is useless at best, and misleading at worst.

This has nothing to do with UML. Ad-hoc diagrams or plain text descriptions become outdated at the same speed, which depends only on the level of detail that you put in documentation and not on the format if it. If you cannot keep up with the changes in the code, you are choosing the wrong level of detail, that’s it.

Ad hoc diagrams are much more likely to be tossed in the trash can after a week. If you keep them longer than the same problems apply. If you only keep them for a week than ad hoc is good enough as everyone still remembers what the symbols mean from when you created it, and the next time it won't matter that the symbols mean something different

I agree with everything you said until you got to UML diagrams. The problem with UML diagrams is that they communicate exactly the same thing that the code should be communicating. Class diagrams are not higher-level than the code they describe. Instead, communicate high-level intent and interactions.

> Mature teams write code.

Sounds very Dunning-Krugerish “smart people like me do X and not smart people do Y”

Coding and documenting aren’t exclusive. Modeling is part of documenting. UML is a type of modeling.

I would think effective teams will want to build good software. And to build good software they’ll want to capture requirements, communicate with other teams, and test their software. Design helps with this and is part of coding.

At the end of a successful day, I should have some updated models, some code, and some running software. If someone wants to see what I did, they’d likely read through different parts.

Just like trying to figure out a stage by just reading models sucks, so does trying to figure it out by just running the software.

UML is not documentation, it's code for people who can't read code. UML diagrams offer no additional information to someone who already can read code (and write readable code). They are training wheels. Mature bike riders don't use training wheels. Mature teams don't write UML -- they write code instead.

Other forms of documentation have their own tradeoffs, but I was not discussing those. You're the one who automatically equated UML with all possible documentation.

> to build good software they’ll want to capture requirements, communicate with other teams, and test their software

UML is awful at all of this.

> At the end of a successful day, I should have ...

> “smart people like me do X and not smart people do Y”

You don't see the irony here?

Mature teams document their code

With the odd caveat that you probably use sketches of these diagrams? As soon as you are trying to cram in all of the extra details stuff like class diagrams can do, you are probably wasting time.

I do not understand your question. If I do not deviate from convention but omit unimportant details, is it a sketch for you?

If you have a project document template from PMBoK, do you feel obliged to fill all the sections or you document only information relevant to your project? With UML it’s the same: it offers a lot, but you do not have to use everything to produce a conforming diagram.

It it a sketch if you don't include every detail that UML was specifically designed to convey? Yeah? Noting that a sketch is not a derogatory phrase here.

Note that, for many of these diagrams, they existed before UML. It was an attempt to formalize them. In classes, they are often used as code generation tools in an attempt to keep a 1:1 between document and code. Laudable, but I have yet to see that work out well.

To your point, I think, the same ultimately goes for document templates. Way too many are used prescriptively as a way to make a successful project. Much to the chagrin of the document writer when the project fails. Often miserably. To the point that I'm convinced most accurate project documents are after the fact. Certainly not waterfall to the project that they are describing.

>I think it mostly depends on maturity of the team

yep. kids out of college feel most inclined to use it.