There are domains where C# (and F#) productivity stems from similar reasons why writing a game in something that isn't Rust might be more productive without even sacrificing performance (or, at least, not to the drastic extent).
I can give you an example:
var number = 0;
var delay = Task.Delay(1000);
for (var i = 0; i < 10; i++)
{
Task.Run(() =>
{
while (!delay.IsCompleted)
{
Interlocked.Increment(ref number);
}
});
}
await delay;
How would you write this idiomatically in Rust without using unsafe?
To avoid misunderstanding, I think Rust is a great language and even if you are a C# developer who does not plan to actively use it, learning Rust is of great benefit still because it forces you to tackle the concepts that implicitly underpin C#/F# in an explicit way.
There's a few things here that make this hard in Rust:
First, the main controller may panic and die, leaving all those tasks still running; while they run, they still access the two local variables, `number` and `delay`, which are now out of scope. My best understanding is that this doesn't result in undefined behavior in C#, but it's going to be some sort of crash with unpredictable results.
I think the expectation is that tasks use all cores, so the tasks also have to be essentially Send + 'static, which kinda complicates everything in Rust. Some sort of scoped spawning would help, but that doesn't seem to be part of core Tokio.
In C#, the number variable is a simple integer, and while updating it is done safely, there's nothing that forces the programmer to use Interlocked.Read or anything like that. So the value is going to be potentially stale. In Rust, it has to be declared atomic at the start.
Despite the `await delay`, there's nothing that awaits the tasks to finish; that counter is going to continue incrementing for a while even after `await delay`, and if its value is fetched multiple times in the main task, it's going to give different results.
In C#, the increment is done in Acquire-Release mode. Given nothing waits for tasks to complete, perhaps I'd be happy with Relaxed increments and reads.
So in conclusion: I agree, but I think you're arguing against Async Rust, rather than Rust. If so, that's fair. It's pretty much universally agreed that Async Rust is difficult and not very ergonomic right now.
On the other hand, I'm happy Rust forced me to go through the issues, and now I understand the potential pitfalls and performance implications a C#-like solution would have.
Does this lead to the decision fatigue you mention in another sub-thread? It seems like it would, so I'll give you that.
For posterity, here's the Rust version I arrived at:
let number = Arc::new(AtomicUsize::new(0));
let finished = Arc::new(AtomicBool::new(false));
let finished_clone = Arc::clone(&finished);
let delay = task::spawn(async move {
sleep(Duration::from_secs(1)).await;
finished_clone.store(true, Ordering::Release);
});
for _ in 0..10 {
let number_clone = Arc::clone(&number);
let finished_clone = Arc::clone(&finished);
task::spawn(async move {
while !finished_clone.load(Ordering::Acquire) {
number_clone.fetch_add(1, Ordering::SeqCst);
task::yield_now().await;
}
});
}
delay.await.unwrap();
use std::{
sync::{
Arc,
atomic::{AtomicBool, AtomicUsize, Ordering},
},
time::Duration,
};
fn main() {
let num = Arc::new(AtomicUsize::new(0));
let finished = Arc::new(AtomicBool::new(false));
for _ in 0..10 {
std::thread::spawn({
let num = num.clone();
let finished = finished.clone();
move || {
while !finished.load(Ordering::SeqCst) {
num.fetch_add(1, Ordering::SeqCst);
}
}
});
}
std::thread::sleep(Duration::from_millis(1000));
finished.store(true, Ordering::SeqCst);
}
What if we want to avoid explicitly spawning threads and blocking the current one every time we do this? Task.Run does not create a new thread besides those that are already in the threadpool (which can auto-scale, sure, but you get the idea, assuming the use of Tokio here).
Even when it's used by mediocre developers, which is probably more than 90% of us, myself very much included? All I've been seeing is Rust being used by very enthusiastic and/or talented developers, who will be productive in any language.
If your baseline is a language that is missing some features that were in standard ML, sure. If you were already using OCaml or F#, Rust doesn't make you any more productive. If you were already using Haskell or Scala, Rust's lack of HKT will actively slow you down.
Longer compile times prolong iterative programming processes and having to take care of memory management through linear types adds restrictions on how you can express code and leads to additional mental burden. This can be part of a trade-off, where you get things in return (no runtime/gc), but your typical web app I don't see much advantages.
Where have you been the past 5 years? Rust developers are insanely productive.
Can we put this myth to rest already? Rust being an "unproductive language" is thoroughly dis-proven.