Rust is the only language I know of that is actively being used at the kernel level all the way through to the web app level. Compare that with Swift which is not only mostly tied to a single ecosystem, but even the "cross platform" stuff like libdispatch is littered with code like:

if #available(macOS 10.12, iOS 10.0, tvOS 10.0, watchOS 3.0, *)

Swift has little to no use outside the apple ecosystem, and even if you are currently using Apple, you have to consider your targets as well. Writing in Swift means your code will only be usable by other Apple users, which is canonically a rather small fraction of technology users. Rust on the other hand is multiplatform and super low level, there's very few other languages out there that can match the potential of applications of rust code. Thus you will, in time, be introduced to many other technologies as well, like AI/ML, low level programming, web, integrations between languages, IoT, those are only a few of all the possibilities. On the other hand, even if Swift has a much more mature ecosystem, it's still only good for creating UIs in all things Apple, which is pretty telling; Apple is not willing to put in the time and effort to open it's language to other fields, because it sees no value in them being the ones providing the tooling for other purposes. They pretty much only want people to code web apps for them, and Swift delivers just fine for that. So if your current purpose is making Apple UIs, you could learn Swift, but be warned that either you'll either be doing that your whole life or will eventually be forced to change languages again.

Then again, most languages nowadays aren't that different from each other. I can code in a truckload of languages, not because I actually spent time making something coherent and complete with each one of them, but because I know some underlying concepts that all programming languages follow, like OOP, or functional programming, and whatever those entail. If you learn those you will not be afraid to switch languages on a whim, because you'll know you can get familiar with any of them within a day.

I think rust is good for learning some low level concepts, especially coming from python.

I don’t think Python is going anywhere in the ML space though.

Other than having first class support on Apple's hardware Swift dosen't have much going for it. There is no killer feature in Swift, it dosen't widespread features and it only has a small niche. If you want to develop for mainly Apple devices I would say go for it as that is the niche it was designed for. Although I see from your post you want to do ML, Python for the high level stuff + C++ for the low level stuff is probably your best pick for that. May I ask what type of ML are you going for? Are you mainly using libraries like Tensorflow, Pytorch etc... or are you into the nitty gritty of building these things yourself and writing the required code for the matrix math and training algorithms.

I think Python is still unmatched when it comes to ML, and nothing can beat Swift in terms of Apple ecosystem support. Why not learn both, though? I find Swift a bit harder to reason with than rust, but both have merit (and both have interesting use cases). Just see what uses you will find for them as you progress.

If you're trying to prepare for a couple of years in advance, it might be worth spending a day playing with each language just to see which one feels best to you. Both languages should be able to do anything you want but some things will probably be more difficult in one or the other. I've never used swift, but I know rust can have a rather steep learning curve. That may be deterrent enough for some people, but that's up to you to decide if that struggle is worth it.

If you don't have a Mac I don't think you can get the MacOS SDK.

So in that case I'd recommend Rust. I still think most of Rust's tools/frameworks need more time in the oven but Rust is massive and has tools being built for everything. If you want Mobile I'd recommend you take a look at Dioxus or Tauri. There are probably others as well but I don't know them it's been a while since I've looked.

Pascal

@Bluetreefrog
I, like you, code for myself not others and not professionally. Take a dive into Xcode and Swift if you're in the Apple world. It is just stupid easy to throw together an app or tool in no time at all.

Julia

Something to consider as well is learning both. Swift is certainly the best choice for making macOS/iOS GUIs. Other languages are probably better than Swift for your ML needs (could be rust, Python, etc.). However it’s totally possible to have an app using multiple languages. You could have the UI portion be in Swift, but the ML portions be in another language.

At my company we have a Mac app with the GUI written in Swift, shared logic with our Windows app written in C++, and some libraries written in Rust. So it’s certainly possible.

One caveat is that some languages don’t work with each other very well. Swift and Python do work well together iirc, so doing UI code in Swift and ML code in Python may not be a bad idea.

If you want to just stick to Swift, Apple does have some ML frameworks for Swift that you can use. I don’t do any work with ML, so I have no idea if these frameworks are any good, or have good resources for learning.

If you want to just stick with whatever language you use for ML, there are GUI libraries in nearly every language. These certainly won’t be as robust or as nice to work with as the native frameworks in Swift, but they could probably get the job done. I do know that a major issue with GUIs in Python is the difficulty in multi threading, which is a must for any app that performs long tasks without the UI freezing.