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Mixed feelings on Rust

· 16 min read
Matej Focko

Rust has become a rather popular language these days. I've managed to get my hands dirty with it during Advent of Code ‘22 and partially ‘23. I've also used it for few rounds of Codeforces and I have to try very hard to maintain some variety of languages for LeetCode challenges along with the Rust. I'll disclaim up front that I won't be only positive, since this post is a result of multiple discussions about Rust and I stand by “All that glitters is not gold”, so if you can't stand your favorite language being criticized in any way, don't even proceed. 😉

Memory safety

I'll start by kicking the biggest benefit of the language, the memory safety. Let's be honest here, majority of the checks rely on the static analysis, cause you can't do anything else during the compile-time, right? Therefore we can basically say that we are relying on the compiler to “solve” all of our issues.


I'm not doubting the fact that compiler can prevent a lot of the memory errors, I'm just saying it's not realistic to cover everything.


I guess we can safely1 agree on the fact that we 100% rely on the compiler to have our back. Is the compiler bug-free? I doubt it. This is not meant in an offensive way to the Rust compiler developers, but we need to be realistic here. It's a compiler, even older and larger projects like gcc or llvm can't avoid bugs to appear.

When I was trying out Rust for some of the LeetCode challenges I've stumbled upon the following warning: Example of a compiler bug

The issue here comes from the fact that we have 2 simultaneous references to the same memory (one is mutable and one immutable). If you cannot think of any way this can break, I'll give you a rather simple example from C++ where this could cause an issue.

Imagine a function that has some complex object and also calls a coroutine which utilizes read-only reference to that object. When the coroutine suspends, the caller can modify the object. This can break the integrity of data read by the coroutine.

  • Yes, this can cause a memory error.
  • Yes, this hasn't been handled until someone noticed it.

Fixing this bug is not backwards compatible, cause you're covering a case that hasn't been covered before.

Enforcing the safety

One of the ways Rust enforces the safety is by restricting what you can do, like the example above. Aforementioned issue can happen, but doesn't have to. Rule of the thumb in the Rust compiler is to “block” anything that can be an issue, static analysis can't do much more, it cannot decide whether it's safe to do it or not.

Satisfying the Rust compiler is sometimes a brutal pain in the ass, because you cannot do things like you're used to, you need to work around them somehow.


Key difference between Rust and C or C++ lies in the fact that Rust chooses to ban all “potentially offensive” actions, C and C++ relies on you to be sure it's safe to do.

C++ v. Rust


Where are we heading with this approach of “if it compiles, it runs” though? In this aspect I have a rather similar opinion as with regards to the ChatGPT and its derivatives.

If you teach people to 100% depend on the compiler, they will do it, cause it's easy. All you need to do is make the compiler shut up2. Giving up the intellectual masturbation about the memory safety will make you lose your edge over the time. When we get to the point of everyone being in the mindset mentioned above, who's going to maintain the compiler? This is the place where you need to think about the memory safety and furthermore in a much more general way than in your own projects, because it is the thing that everyone blindly believes in in the end.

I'm not saying that everyone should give up Rust and think about their memory management and potential memory issues. I'm just saying that going the easy way will make people dull and they should think about it anyways, that's how the issue above has been discovered. If everyone walked past and didn't think about it, no one would discover this issue till it bit them hard.

Standard library

Even the standard library is littered with unsafe blocks that are prefixed with comments in style:

// SAFETY: …

The fact that the casual Rust dev doesn't have to think much about safety, cause the compiler has their back, doesn't mean that the Rust compiler dev doesn't either.

I gotta admit that I adopted this concept in other languages (even in Python), cause you can encounter situations where it doesn't have to be clear why you can do what you're doing.

Development & design

Development of Rust is… very fast. One positive is that they're trying to be as backward compatible as possible at least by verifying against all the published crates in the process. Of course, you cannot be backward compatible about fixing the bugs that have been found, but such is life.

Fast development cycle

One of the negatives of the fast development cycle is the fact that they're using the latest features already in the next release of the Rust. Yes, it is something that you can use for verifying and testing your own changes, but at the same time it places a requirement of the latest release to compile the next one.


If you check gcc for example, they have a requirement of minimal version of compiler that you need for the build. Though gcc's requirement is not so needy as the Rust one.

One of the other negatives is the introduction of bugs. If you're pushing changes, somewhat mindlessly, at such a fast pace, it is inevitable to introduce a bunch bugs in the process. Checking the GitHub issue tracker with

is:issue is:open label:C-bug label:T-compiler

yields 2,224 open issues at the time of writing this post.


You can find a lot of RFCs for the Rust. Some of them are more questionable than the others. Fun thing is that a lot of them make it to the nightly builds, so they can be tested and polished off. Even the questionable ones… I'll leave few examples for a better understanding.

One of such features is the do yeet expression:


fn foo() -> Result<String, i32> {
do yeet 4;
assert_eq!(foo(), Err(4));

fn bar() -> Option<String> {
do yeet;
assert_eq!(bar(), None);

It allows you to “yeet” the errors out of the functions that return Result or Option.

One of the more recent ones is the ability to include Cargo manifests into the sources, so you can do something like:

#!/usr/bin/env cargo
clap = { version = "4.2", features = ["derive"] }

use clap::Parser;

#[derive(Parser, Debug)]
struct Args {
#[clap(short, long, help = "Path to config")]
config: Option<std::path::PathBuf>,

fn main() {
let args = Args::parse();
println!("{:?}", args);

I would say you can get almost anything into the language…

Community and hype train

Rust community is a rather unique thing. A lot of people will hate me for this, but I can't help, but to compare them to militant vegans. I'll go through some of the things related to it, so I can support my opinion at least.

Rust is the best language. It is not. There is no best language, each has its own positives and negatives, you need to choose the language that's the most suitable for your use case. There are areas where Rust excels, though I have to admit it's very close to being a universal hammer regardless of how suitable it is. There is a very steep learning curve to it, beginnings in Rust are very painful.

Rewrite everything in Rust. Just no. There are multiple feedbacks on doing rewrites, it is very common to fix N bugs with a rewrite while introducing N + 1 other bugs in the process. It doesn't solve anything unless there are some strong reasons to go with it. Majority of such suggested rewrites don't have those reasons though.

Language ‹x› is bad, though in Rust… Cherry-picking one specific pain point of one language and reflecting how it is better in other language can go both ways. For example it is rather easy to pick the limitations imposed by Rust compiler and show how it's possible in other languages 🤷‍♂️

I don't mind any of those opinions, you're free to have them, as long as you don't rub them in my face which is not the usual case… This experience makes it just worse for me, part of this post may be also influenced by this fact.

Rust in Linux


As someone who has seen the way Linux kernel is built in the RHEL ecosystem, how complex the whole thing is and how much resources you need to proceed, I have very strong opinions on this topic.

It took years of work to even “incorporate” Rust into the Linux codebase, just to get the “Hello World!”. I don't have anything against the idea of writing drivers in the Rust, I bet it can catch a lot of common mistakes, but still introducing Rust to the kernel is another step to enlarge the monster.

I have to admit though that the Apple GPU driver for Linux written in Rust is quite impressive. Apart from that there are not so many benefits, yet…


I'll divide the packaging into the packaging of the language itself and the programs written in Rust.

Let's start with the cargo itself though. Package managers of the languages usually get a lot of hate (you can take npm or pip as examples3). If you've ever tried out Rust, I bet you already know where I'm going with this. Yes, I mean the compilation times, or even Cargo downloading whole index of crates just so you can update that one dependency (and 3 millions of indirect deps). When I was doing AoC ‘22 in Rust, I've set up sccache right away on the first day.

Let's move to the packaging of the Rust itself, it's tedious. Rust has a very fast development cycle and doesn't even try to make the builds backward compatible. If there is a new release of Rust, there is a very high chance that you cannot build that release with anything other than the latest Rust release. If you have ever touched the packaging, you know that this is something that can cause a lot of problems, cause you need the second-to-latest version to compile the latest version, don't forget that this applies inductively… People running Gentoo could tell you a lot about this.


Compiling the compilers takes usually more time than compiling the kernel itself…

I cannot speak about packaging of Rust programs in other than RHEL-based distros, though I can speak about RHEL ecosystem. Fedora packaging guidelines specify that you need to build each and every dependency of the program separately. I wanted to try out AlmaLinux and install Alacritty there and I failed miserably. The solution that worked, consisted of ignoring the packaging guidelines, running cargo build and consuming the binaries afterwards. Dependencies of the Rust programs are of a similar nature as JS dependencies.

I'm tipping my fedora1 in the general direction of the maintainers of Rust packages in RHEL ecosystem. I wouldn't be able to do this without losing my sanity.


If you've come all the way here and you're a Rustacean, I believe I've managed to get your blood boiling, so it's time to finish this off by stuff I like about Rust. I doubt I will be able to cover everything, but I can try at least. You have to admit it's much easier to remember the bad stuff as opposed to the good. 😉

Workflow and toolchain

I prefered using Rust for the Advent of Code and Codeforces as it provides a rather easy way to test the solutions before running them with the challenge input (or test runner). I can give an example from the Advent of Code:

use aoc_2023::*;

type Output1 = i32;
type Output2 = Output1;

struct DayXX {}
impl Solution<Output1, Output2> for DayXX {
fn new<P: AsRef<Path>>(pathname: P) -> Self {
let lines: Vec<String> = file_to_lines(pathname);


fn part_1(&mut self) -> Output1 {

fn part_2(&mut self) -> Output2 {

fn main() -> Result<()> {

test_sample!(day_XX, DayXX, 42, 69);

This was the skeleton I've used and the macro at the end is my own creation that expands to:

mod day_XX {
use super::*;

fn part_1() {
let path = DayXX::get_sample(1);
let mut day = DayXX::new(path);
assert_eq!(day.part_1(), 42);

fn part_2() {
let path = DayXX::get_sample(2);
let mut day = DayXX::new(path);
assert_eq!(day.part_2(), 69);

When you're solving the problem, all you need to do is switch between cargo test and cargo run to check the answer to either sample or the challenge input itself.

Introduce bacon and it gets even better. Bacon is a CLI tool that wraps around the cargo and allows you to check, run, lint or run tests on each file save. It's a very pleasant thing for a so-called compiler-assisted development.

Speaking of linting from within the bacon, you cannot leave out the clippy. Not only it can whip your ass because of errors, but it can also produce a lot of helpful suggestions, for example passing slices by borrow instead of borrowing the Vec itself when you don't need it.

Standard library

There's a lot included in the standard library. It almost feels like you have all you need4. I like placeholders (like todo!(), unreachable!(), unimplemented!()) to the extent of implementing them as exceptions in C++.

You can find almost anything. Though you can also hit some very weird issues with some of the nuances of the type system.


This might be something that people like to avoid as much as possible. However I think that forming a habit of commenting posibly unsafe operations in any language is a good habit, as I've mentioned above. You should be able to argue why you can do something safely, even if the compiler is not kicking your ass because of it.

Excerpt of such comment from work:

# SAFETY: Taking first package instead of specific package should be
# safe, since we have put a requirement on »one« ‹upstream_project_url›
# per Packit config, i.e. even if we're dealing with a monorepo, there
# is only »one« upstream. If there is one upstream, there is only one
# set of GPG keys that can be allowed.
return self.downstream_config.packages[


One of the other things I like are the traits. They are more restrictive than templates or concepts in C++, but they're doing their job pretty good. If you are building library and require multiple traits to be satisfied it means a lot of copy-paste, but that's soon to be fixed by the trait aliases.

Comparing to other languages

On Wikipedia I've seen trait being defined as a more restrictive type class as you may know it from the Haskell for example. C++ isn't behind either with its constraints and concepts. I would say that we can order them in the following order based on the complexity they can express:

Rust's trait < Haskell's type class < C++'s concept

You can also hit some issues, like me when trying to support conversions between underlying numeric types of a 2D vectors or support for using an operator from both sides (I couldn't get c * u to work in the same way as u * c because the first one requires you to implement the trait of a built-in type).


Implementing traits lies in

impl SomeTrait for SomeStruct {
// implementation goes here

One of the things I would love to see is being able to define the helper functions within the same block. As of now, the only things allowed are the ones that are required by the trait, which in the end results in a randomly lying functions around (or in a implementation of the structure itself). I don't like this mess at all…

Influence of functional paradigm

You can see a big influence of the functional paradigm. Not only in iterators, but also in the other parts of the language. For example I prefer Option<T> or Result<T, E> to nulls and exceptions. Pattern matching together with compiler both enforces handling of the errors and rather user-friendly way of doing it.

Not to mention .and_then() and such. However spending most of the time with the AoC you get pretty annoyed of the repetitive .unwrap() during parsing, since you are guaranteed correct input.


Macros are a very strong pro of the Rust. And no, we're not going to talk about the procedural macros…

As I've shown above I've managed to “tame” a lot of copy-paste in the tests for the AoC by utilizing a macro that generated a very basic template for the tests.

As I have mentioned the traits above, I cannot forget to give props to derive macro that allows you to “deduce” the default implementation. It is very helpful for a tedious tasks like implementing Debug (for printing out the structures) or comparisons, though with the comparisons you need to be careful about the default implementation, it has already bitten me once or twice.


Overall there are many things about the Rust I like and would love to see them implemented in other languages. However there are also many things I don't like. Nothing is exclusively black and white.


  1. pun intended 2

  2. It's not that easy with the Rust compiler, but OK…

  3. not to even mention multiple different packaging standards Python has, which is borderline

  4. unlike Python where there's whole universe in the language itself, yet there are essential things not present…