From the article it seems Rust is really a great replacement for C++ and all it's complexity and quirks. I wonder how many other C++ projects are considering moving to it, anyone know about any major one like FF?
If you start learning C++ it's relatively smooth sailing at first, especially if you're already familiar with C. Basic OOP, basic RAII, inheritance, virtual functions, basic templates. Easy peasy.
It's once you start getting to the advanced topics that the footguns become apparent. The sometimes intricate resolution rules (and how they compound with template substitution rules), the various subtleties surrounding copy constructors, const, mutable, concurrency and the way they play with each others, the various quirks inherited from C that sometimes don't play very well with modern constructs etc...
Rust is the other way around. There's a very steep curve right at the start where you need to understand how the borrow checker works and how to make it happy. You have to learn the right mindset right away. You need to get over that to reach the "fearless confidence" goodness.
I think that's going to be a big problem for experienced C++ coders to do the jump (especially if you need to convince multiple devs to make the jump at the same time).
It kind of reminds me of the switch from SVN to git. At first I didn't get it, git felt a lot more complicated and I didn't really see the benefit compared to good old SVN. Of course after a few years I'd curse under my breath every time I had to use SVN for some legacy codebase, it feels so clunky and limited now that I'm familiar with a proper git workflow.
This is probably the point that simias is making and I tend to agree. It's straightforward to get a simple C++ program working with decent performance if you know C. And RAII, std::vec etc makes you feel quite productive.
Now, at some point you'll notice that debug and release don't act the same way. Occasionally. Or you try to add threading to a single-threaded program. Then the love will die (due to bloodloss from blowing off the whole leg). But that's often after months of reasonably productive development.
Rust, to a large extent, will prevent you from ever getting to that state and that's a very good thing. But the upfront cost is quite high. My guess is that those of us who have experienced the C++ pain will appreciate the value that that cost is buying.
But I'm hopeful that Rust will draw a wider audience primarily because of your last point. It's really quite conservative at present. The NLS work is already expanding the scope of acceptable programs and, I presume, that what is learnt from that effort will seed further work in that space.
It's only when you start to have all these elements work (or not work) together that you realize that it's not as simple as it first seemed and the various side effects, overloadings and implied constraints sprinkled throughout the code turned it into a virtual minefield.
Case in point, this video I've watched the past week: https://channel9.msdn.com/posts/C-and-Beyond-2012-Herb-Sutte...
It's a very interesting talk (and probably worth a watch if you're a C++ developer) but the amusing thing to me is that he begins by showing two short pieces of rather simple C++ code and asks the audience if they are UB or not. Seems like nobody can (or want to) answer that question.
Spoiler: the conclusion of the talk is that one of these pieces of code is only legal if the copy constructor of the custom type adheres to certain implied constraints that are not enforced by the compiler and, it seems, few people are aware of.
Of course it turns out that it's a lot more complicated and powerful than that and it's probably the wrong way to look at C++ but it might take a while until you realize that you're not in Kansas anymore. Rust on the other hand forces you to become acquainted with its paradigm right away, unless you're willing to put all your code in unsafe blocks.
Rust is a clear winner over either in my view because of its traits system and immutable-by-default story. It feels like the kind of C++ I write, but with less boilerplate and typing. The safety story is irrelevant in our case (it's nice, but wasn't an explicit factor in the decision: the other features in Rust may have been developed to support safety, but safety need not exist to provide them). The biggest pain point is that it's not an appropriate language for high performance numerical computation, so we'll have some "glue" there. How that will work is yet to be determined, but the data engineering and infrastructure around the pipeline is definitely going to Rust.