How lightweight can a desktop environment based on QT be? I thought QT is a rather hefty dependency.

Qt is not big and is well architected, so you should not have issues with a Qt based DE but you could stop useless services to get more performance. Qt will not eat your CPU or RAM but if you have a very old device you probably want to use some OS designed for that type of hardware or use KDE3

> Qt is not big and is well architected

I've used Qt in the past and current. Qt is big and, while it might be sufficiently architected, I wouldn't describe it as well architected. There's a lot of Qt-isms that don't follow modern C++ paradigms. The concept of shallow- and deep- copy is particularly frustrating, everything that's based in QObject can't be moved, and a lot of the objects simply _aren't_ extensible enough. Qt's QNetworkAccessManager is probably one of the least-acceptable (or extensible) network access libraries; good luck adding support for custom types of proxies or schemes.

What do you mean is big? How much % of your RAM will a Qt application take?

What I mean by well architected is that:

1 it respects the user choice so it tries to use the user themes, icons , fonts (it would do a even better job if Miscrosoft and Apple would contribute a bit when they change their designs)

2 it is efficient, it does not use some hacky stuff like you see in angular or react, where one click causes some data to change then a lot of code runs and check what changed where, then try see what other data needs to change then finally updates the DOM, which DOM is a super complex piece of software that is super easy to eat a lot of CPU with just a line of CSS or cause a lot of recalculations when you update one item.

3 Qt gives you a lot of widgets to build on top of, I remember it had a lot of APIs not only for GUI but also networking, desktop integration(like to use the native notifications)

4 I loved the fact Qt had it's own standard library, I know some c++ purists won't like that and the qmake , but we need to understand how many platforms Qt targeted and that the col new C++ features were not there on all this platforms when Qt4 was created (and even with Qt4 I think there was a way to upgrade from Qt3 so there was not a complete start from scratch).

I assume there are some smaller toolkits, there are some posted here but I think the smaller ones have only 20% of the features.

IMO the reason Qt is not used as much is because it uses C++ , for modern application I think developers prefer garbage collected languages and Qt (last time I checked) did not had mature bindings for this popular languages.

Sorry for the long comment, what would you use today if you need to make an application for someone, something simple like some buttons, menus and it does a bit of work maybe with some files or the internet), the goal is to be fast and have very few bugs that you will have to support by fixing them.

Indeed so! Qt is living today with the fact that it was built and designed long before C++11 was really a thing (where C++11 is the baseline of modern C++ and I would argue that even C++17 should be considered the baseline). The design decisions of Qt are directly against modern C++ design. I think that's ultimately the core of the problem: that modern Qt is orthogonal, not complementary, to modern C++.

Range-for loop? Oops, accidentally detached and deep-copied into a temporary.

Move objects? Just, no.

unique_ptr? Nah, QScopedPointer. Also still not moveable. make_unique? Nah, reset(new...) and ignore the modern advice that you shouldn't use `new`

Qt still takes naked pointers and decides willy-nilly whether to take ownership. It still has examples everywhere for using naked new without even mentioning the context of a smart pointer. It has the concept of "you used new, but the parent actually owns it, unless the parent is null" which is just a time bomb for anyone new to the framework let alone the language.

No, there's no way I would recommend Qt to someone who isn't experienced. Since I wouldn't recommend it then it's no wonder to me why Qt isn't used so much. It has little to do with C++ and a lot more to do with the design decisions of Qt itself.

> IMO the reason Qt is not used as much is because it uses C++

Arguably. Also arguably is because Qt brings along a lot of unnecessary baggage. You mentioned using Qt requires using qmake (which definitely counts as arcane, if not archaic); cmake does a pretty good job of wrapping qmake but doesn't eliminate it. And all of that is because of Qt's non-standard magical signals & slots system which is really just a more error-prone semi-async system when compared to any other eventing system.

Using Qt efficiently strongly needs Qt Creator which isn't nearly as good as Visual Studio or VS Code and not as feature-rich as CLion or other intellij-based IDEs I've used -- but at least it performans way better than CLion or intellij trash.

Qt's license changing in 5.15 has also become a significant penalty to non-commercial use. This fact alone means there's no way I'd use Qt in a new project, even a commercial one.

Modern Qt developers also have to become javascript developers since Qt's UI is heavily driving towards QML. That's an unfortunate direction and also inhibits adoption of Qt IMO. Why write an application in C++ if you need to learn javascript anyway? There are better feature-rich javascript frameworks with better community adoption and better price points.

> what would you use today if you need to make an application for someone, something simple like some buttons, menus and it does a bit of work maybe with some files or the internet), the goal is to be fast and have very few bugs that you will have to support by fixing them

For GUI, Dear Imgui [0].

For network, Asio [1].

For files, plain standard streams. They're not fast but if your files are your bottleneck then I'd consider memory-mapped files.

[0]: https://github.com/ocornut/imgui

[1]: https://www.boost.org/doc/libs/1_77_0/doc/html/boost_asio/re...