brassica VS QMetaObject crate for Rust

I’ve done something like this before to call Haskell from C++ (in [0]), so that I can build my GUI using Qt. It worked pretty well, except that I ran into various difficult-to-resolve linking problems on both Windows and Linux. After a year or two of trying to maintain it, I gave up and switched to a protocol where both sides pass JSON over stdin/stdout. This particular piece of software doesn’t require a huge amount of communication or shared data, so it works well enough.

The really nice thing about the original interop code, though, is that GHC’s new WASM backend uses essentially the same foreign function interface to export functions to JavaScript. So with only some minor modifications, I was able to get the same program working on a webpage [1], which I think is pretty cool.

[0] https://github.com/bradrn/brassica

[1] At the risk of DDOS’ing my poor little home server: https://bradrn.com/brassica/

GHC’s WASM backend is already really useful! I also used it to port one of my own programs to the browser [0], albeit not using the DOM as this person did. Documentation is still sparse, but it’s a very similar process to creating a shared foreign library.

[0] https://github.com/bradrn/brassica

No experience with Rust, but for a couple of personal projects I’ve written the logic in Haskell and the GUI in C++ (e.g. https://github.com/bradrn/brassica/blob/master/ARCHITECTURE....). It works pretty well, at least for smaller projects — the basic idea is that the Haskell code gets compiled into a library (static on Windows, dynamic on Linux) which the C++ side can link to. I’d imagine doing the same with Rust would be even easier, since it’s less of a pain to marshal stuff across the language barrier.

The biggest one for me is undoubtedly my custom keyboard layout Conkey [0], which I use constantly (including for typing this very comment). I hate the way the base US layout tends to get distorted in other keyboard layouts with good support for non-ASCII characters, so Conkey had the explicit goal of retaining that basic unshifted layout. I’ve also ended up porting Conkey to Mac and Linux — and given that I’m slowly switching from Windows to Linux, at least the Linux ports have ‘scratched my own itch’ too, which is nice.

Also, I made a utility to archive the full text of every website I view and store it in a SQLite database for searching. It’s proven pretty useful when I want to find something I saw a while ago and then forgot. (I haven’t attempted to open-source it, though — it consists of three entirely separate components, two of which were a pain to set up. I must try to get it into a more usable state one of these days.)

What else… my sound change applier [1], perhaps? Not that I use it very much, because I only need it on those occasions when I want to do some conlanging, which I haven’t had much time for recently. Actually, sound change appliers strike me as being very much a ‘scratch own itch’ type of project in general… sometimes it feels like every conlanger has written their own, and no two can agree on a nice design. Everyone just has their own unique preferred way of doing things.

[0] https://github.com/bradrn/Conkey

[1] https://github.com/bradrn/brassica

Recently I’ve been trying to do some GTK+ programming again, as a change from my more recent attempts to use Qt with Haskell. Alas, when I try to build the example application from the documentation, I get an error:

You can use Rust with QML[1].

QML is actually pretty amazing. I've been building my block editor[2] view entirely in QML while the model is in C++. This separation of logic and presentation works great. And yes, there are some crashes sometimes (that I find quite easy to debug thanks to the built-in debugger), but take for example a similar app that's built with Rust and Dart[3], in my testing there were still memory leaks that caused my computer to hang. It's better to know you have a bug than for it to be hidden from you.

I agree with parent commenter, saying these cross-platform frameworks will end up supporting the least common denominator set of features. But I found with external open source libraries, the community is catching up very fast. For example, you want the awesome translucency macOS apps have for your Qt app? Here you go[4]. Many such cases. It's also pretty straightforward to add your own custom OS-dependent code, especially so, if someone already open sourced his approach. I recently wanted to move the traffic light buttons on macOS for my app, but couldn't figure the Objective-C code for that. I ended up looking at either Tauri or Electron source code and found my answer.

[1] https://github.com/woboq/qmetaobject-rs

[2] https://www.get-plume.com/

[3] https://www.appflowy.io/

[4] https://github.com/stdware/qwindowkit

I just used qmetaobject-rs and my experience with Qt/QML. There's the QML book from Qt if you're just starting, which is pretty nice https://www.qt.io/product/qt6/qml-book

qmetaobject is probably the most mature Qt Rust binding at the moment. It uses the cpp crate to embed C++ inline in Rust to create its bindings. There are some people using it and it does get some maintenance, but it's not under active development since the original author is now working on Slint.

The bindings currently use the git version of qttypes since I had to merge some upstream changes that are needed for these bindings. So they are not ready for prime time just yet.

There are a bunch of bindings with different language, but even the ones that are officially supported like PySide will still be second class citizen and awkward to use.

Automated binding generation will never give you idiomatic API in whatever language. And if you want an idiomatic library that wraps Qt, it's going to take a huge amount of work.

Which is why I think restricting to QML makes sense because that's a much smaller API surface. That was the ambition behind my previous crate that exposes QML to rust: https://github.com/woboq/qmetaobject-rs/

But now I've moved on to another GUI project: Slint https://github.com/slint-ui/slint

Whisperfish does this with Qt: https://github.com/woboq/qmetaobject-rs/issues/102

What do you want to know? It's pretty easy thanks to the amazing work of guys behind qmetaobject-rs.

This is probably the portion that I found the most difficult. The README of qmetaobject-rs gives us a basic idea of the build script, so I started with that. Here is my starting script