A little context: I got introduced to UML in around 2008, at an employer who had a site licence for Enterprise Architect. I was sent on a training course run by a company that no longer exists called Sun Microsystems: every day for a week I would get on a coach to Marble Arch, then take the central line over to Shoreditch (they were very much ahead of their time, Sun Microsystems) and learn how to decompose systems into objects and represent the static and dynamic properties of these objects on class diagrams, activity diagrams, state diagrams, you name it.
I got a bye on some of the uses of Enterprise Architect at work. Our Unix team was keeping its UML diagrams in configuration management, round-tripping between the diagrams and C++ code to make sure everything was in sync. Because Enterprise Architect didn’t have round-trip support for Objective-C (it still doesn’t), and I was the tech lead for the Mac team, I wasn’t expected to do this.
This freed me from some of the more restrictive constraints imposed on other UML-using teams. My map could be a map, not the territory. Whereas the Unix folks had to show how every single IThing had a ThingImpl so that their diagrams correctly generated the PImpl pattern, my diagrams were free to show only the information relevant to their use as diagrams. Because the diagrams didn’t need to be in configuration management alongside the source, I was free to draw them on whiteboards if I was by a whiteboard and not by the desktop computer that had my installation of Enterprise Architect.
Even though I’d been working with Objective-C for somewhere around six years at this point, this training course along with the experience with EA was the thing that finally made the idea of objects click. I had been fine before with what would now be called the Massive View Controller pattern but then was the Massive App Delegate pattern (MAD software design, if you’ll excuse the ablism).
Apple’s sample code all puts the outlets and actions on the app delegate, so why can’t I? The Big Nerd Ranch book does it, so why can’t I? Oh, the three of us all editing that file has got unwieldy? OK, well let’s make App Delegate categories for the different features in the app and move the methods there.
Engaging with object-oriented design, as distinct from object-oriented programming, let me move past that, and helped me to understand why I might want to define my own classes, and objects that collaborate with each other. It helped me to understand what those classes and objects could be used for (and re-used for).
Of course, these days UML has fallen out of fashion (I still use it, though I’m more likely to have PlantUML installed than EA). In these threads and the linked posts two extreme opinions—along with quite a few in between—are found.
The second is that UML is necessarily part of the heavyweight waterfall go-for-two-years-then-fail-to-ship project management paradigm that The Blessed Cunningham did away with in the Four Commandments of the agile manifesto. Thou shalt not make unto yourselves craven comprehensive documentation!
Neither is true. “We” had a necessary (due to the dot-com recession) refocus on the idea that this software is probably supposed to be for something, that the person we should ask about what it’s for is probably the person who’s paying for it, and we should probably show them something worth their money sooner rather than later. Many people who weren’t using UML before the fall/revelation still aren’t. Many who were doing at management behest are no longer. Many who were because they liked it still are.
But when I last taught object-oriented analysis and design (as distinct, remember, from object-oriented programming), which was in March 2020, the tool to reach for was the UML (we used Visual Paradigm, not plantuml or EA). It is perhaps not embarrassing that the newest tool for the job is from the 1990s (after all, people still teach Functional Programming which is even older). It is perhaps unfortunate that no design (sorry, “emergent” design) is the best practice that has replaced it.
On the other hand, by many quantitative metrics, software is still doing fine, and the whole UML exercise was only a minority pursuit at its peak.