[adastra22]

Also the argument with `Arc<Mutex<Box<T>>>>` boils down to "Rust makes it hard to work with automatic reference-counted shared mutable heap-allocated state." In which case... mission accomplished? Rust just made explicit all the problems that you still have to deal with in any other language, except dealing correctly with all that complexity is such a pain that you will do anything you can to avoid it.

Again, mission f#*@ing accomplished. Maybe you DON'T need that state to be shared, reference-counted, or heap allocated. Maybe you can refactor your code to get rid of those annoyingly hard to deal with abstractions. And you end up with better, more reliable, likely faster code at the end of it.

So many times I've tried to do something in Rust the old fashioned way, the way I have always done things, and been stopped by the compiler. I then investigate why the compiler/language is being so anal about this trivial thing I want to do.. and yup, there's a concurrency bug I never would have thought of! I guess all that old code I wrote has bugs that I didn't know about at the time.

There are basically two reactions people have to this situation: (1) they're thankful that they learned something, their code is improved, and go about their day learning something new; or (2) feel frustrated and helpless that the old way of doing things doesn't work, and rage-quit to go write a "WHY RUST IS THE WORST THING SINCE MOSQUITOS" blog article.

[bryanlarsen]

Nit: it doesn't make it hard, it makes it ugly and explicit. `Arc<Mutex<Box<T>>>>` is not hard to use, it's just annoyingly verbose and ugly.

That's a low level construct, there are much nicer higher level sharing constructs, like channels.

Mission accomplished.

[saghm]

Yeah, this pretty much summarizes my experience. In most situations, the actual information I need to share between different contexts is quite small, and using a channel ends up being pretty clean. There are still times I need an actual reference counted wrapper around a mutex, but they're the exception rather than the norm, and even then, there are often ways you can reduce the contention (e.g. if `T` is a type you can clone, and you only need a snapshot of the current state of the data rather than preventing changes while processing based on that snapshot, you can just clone it, drop the mutex guard, and then proceed without needing to worry about borrows).

[adastra22]

It is hard to use because you can’t just access the shared state. You have to annoyingly lock it, handle the guard object, etc. Each one of those layers has protocols.

[bryanlarsen]

Of course you have to lock a mutex. You'd have to do that no matter the language, right?

And that's what I meant by verbose/ugly. Each of those steps is usually an if let / else error. None of those steps are hard, but you have to do them every time.

[adastra22]

Oh, plenty of people access shared state without proper locks all the time. Even experienced developers.

[bryanlarsen]

Heh. You're pedantically correct, the best kind. I meant "have to" in terms of "for correct operation you must" not "the compiler forces you to" since the latter isn't a thing in some languages.

[saghm]

> So many times I've tried to do something in Rust the old fashioned way, the way I have always done things, and been stopped by the compiler. I then investigate why the compiler/language is being so anal about this trivial thing I want to do.. and yup, there's a concurrency bug I never would have thought of! I guess all that old code I wrote has bugs that I didn't know about at the time.

This is also my experience. I've had dozens of times over the years that I've been confused about why Rust does something a certain way, but I don't think I can recall a single one where I didn't end up finding out that there was an extremely good reason for it. That's not to say that in every one of those cases, the design choice Rust made was the only reasonable one, but in the cases where it wasn't, the situation always ended up being more nuanced than it appeared to me at first glance, and what I would have originally expected would have implicitly made a significant tradeoff I hadn't considered.

I'm having trouble finding it now, but years ago someone had a quote that ended up getting published in the language's weekly newsletter that was something like "Rust moves the pain of understanding your program from the future to the present". It's extremely apt; most of the difficulty I've seen people run into when trying to program in Rust ends up being that they're forced to consider potential issues that in other languages they could have ignored until later, and then would have had to debug down the line.

[adastra22]

That’s a very good quote.

There’s a handful of pain points that the Rust model does impart which are not fundamental. For example, unsafe code is required to get a mutable borrow to two different fields of a struct at the same time.

But really that’s the only example I can think of offhandedly, and I expect there are not many in total. Nearly all of the pain is merely the trouble of thinking through these issue upfront instead of kicking the can down the road.

[saghm]

The only other one I can think of is kind of poor ergonomics around "self-borrows"; it's a lot less common than I've felt the need to mutably borrow two fields from the same struct independently, but there have very occasionally been times where I've realized the simplest way to structure something would be to have one field in a struct borrow another. This is somewhat hard to express given the need to initialize all of the values of a struct at once, and even if you could, there are some complications in how you could use such a struct (e.g. not being able to mutate field `a` safely if it's borrowed by field `b`). Overall though, the things that Rust prevents me from handling safely because of its own limitations rather than them being fundamentally unsafe are quite rare, and even with those, they tend to be things that I would be quite likely to mess up in practice if I tried to do them in a language without the same safety rails.

[byko3y]

>the things that Rust prevents me from handling safely because of its own limitations rather than them being fundamentally unsafe are quite rare, and even with those, they tend to be things that I would be quite likely to mess up in practice if I tried to do them in a language without the same safety rails.

Any language with GC can handle complex links between object, including mutable object. Like Erlang/Elixir, JS, Go, etc. You message implies runtime-less language, but majority of practically employed languages are runtime-full.

[byko3y]

>Maybe you DON'T need that state to be shared, reference-counted, or heap allocated. Maybe you can refactor your code to get rid of those annoyingly hard to deal with abstractions. And you end up with better, more reliable, likely faster code at the end of it.

That's the point 4 in my article — Rust is horrible for mutable shared state. However, in the modern CPU-based programming mutable shared state is like 70% of all the code, so you cannot just ignore it. It's not that CPU-s have to be like that, it's they hapened to be like that.

>there's a concurrency bug I never would have thought of! I guess all that old code I wrote has bugs that I didn't know about at the time.

Programming languages or libraries that excel at concurrency do not use the Arc<Mutex<T>> nuisance. At least they are not imposing it as a main tool. Having shared mutable state does not mean you directly change cell there, like you would in C/C++. I mean if you have a cyclic graph of connected objects — how the hell are you gonna employ Arc<Mutex<T>> for handling them? What Rust actually does is carving in stone pathologic C/C++ ways of "correct handling of shared mutable state" — whatever it is.