I’m still learning Rust, but the idea of having to use unsafe features to implement something as
simple as a linked
list seems “wrong” to me. What am I missing?
Dynamic languages and GC'd languages cover most of what our employers are paying us for: web apps, backend services. It is ironic to build super safe software, then deploying them on kubernetes, written in a GC'd language prone to nil dereference errors.
Rust has its place, but it's a very small place. These days computers are so fast there's companies worth billions built on Ruby and Python, if you go native with a GC language you'll cover 98% of your needs.
Rust IMHO has gone too far towards safety at the expense of developer ergonomics and pragmatism. We're so expensive that adopting a subpar language that is easier to grok is often a savvier business decision.
Indeed. I'm a Rust dev somewhere it actually matters (video dev - we have to process 60 frames a second, for hours/days on end, with completely predictable performance, without crashing once) and I'd never pick it if I just wanted to build a webapp where nothing really matters and if the whole thing falls over we can just put it in a retry loop.
There's plenty of code out there that /cannot/ be written in Ruby/Python/Go/C#. Rust solves some really hard problems for people working on that type of code. But it's not what most people on HN are working on.
I think the problem is that a lot of web developers do not really understand that this type of code exists, and that languages which do not target web development can be exciting.
But without even going as far as frontend web applications, stuff like backend services, system services, GUI applications, CLI applications, etc., don't actually need all that much memory safety and control over allocations.
My understanding is that Rust was designed to be a safe(er) language to write low-level system code than C/C++, not to compete with Python/Ruby/Java for web development applications.
I'm complaining about everybody on programming forums, including HN, seeing Rust as the replacement for most, if not all languages. My opinion is that Rust's ideal problem space is much narrower than people think.
>It is ironic to build super safe software, then deploying them on kubernetes, written in a GC'd language prone to nil dereference errors.
Nil dereference errors don't demonstrate an absence of memory safety. If the runtime checks for a nil reference before dereferencing and then raises an exception, that's perfectly safe.
I don't think the null handling in rust is about memory safety so much as it is their choice in error handling. If you come across a null pointer dereference and your code doesn't handle it, that's a hidden bug. Triggering an exception and handling it is a valid approach, but there are trade-offs. If no code handles the nil exception for example then it's no better than crashing as you would in C. Wrapping things up in try catch can lead to missing recoverable errors or unexpected states. The choice to disallow null is one to avoid common bugs, not one for memory safety, as far as I understand it.
> One common example is modifying a vector element by reference. If you grab a reference to an item, push something else to the vector, then try to access through that reference, the vector may have re allocated during the push and you're either no longer looking at valid memory because it's been freed, or you're looking at a stale copy of the element.
There aren't that many languages which both use GC and allow you to take references to elements of a vector. Go would be one example. I can assure you that you cannot access undefined memory regions by doing this in Go. (What would happen is that the original allocation backing the vector would be retained in addition to the new allocation.)
>If no code handles the nil exception for example then it's no better than crashing as you would in C
C programs are not guaranteed to crash when a pointer has an invalid value. Dereferencing a NULL pointer will reliably cause a crash if you're running the code on top of a modern general purpose operating system with memory protection, but invalid pointers (which don't necessarily have to be NULL) have the potential to access arbitrary memory regions without raising any kind of error.
Current implementation of slices and interfaces in Go is not memory safe in presence of data races:
https://blog.stalkr.net/2022/01/universal-go-exploit-using-d...
Nope, unsafe isn't a way to do dependent typing in Rust.
This is something that escapes a lot of people nowadays.
Everyone uses a browser and they are inherently unsafe.
Meaning that Firefox's gains with Rust will eventually be lost given its market adoption is slowing reaching zero.
https://docs.google.com/document/d/e/2PACX-1vRZr-HJcYmf2Y76D...
https://www.chromium.org/Home/chromium-security/memory-safet...
But yes you are right, anytime you have two or more accesses to a data structure you do have to think a little harder about it. Usually you just want to use a reference to that object, sometimes it makes sense to clone it, sometimes you want to pass it by value and return it by value. In the case of doubly linked lists you probably want to drop into unsafe code.
I get it though, GC languages are more zen in that regard.
Libraries are typically optimized for generic use, so are often more complex, slow, and difficult to extend with new features (both coding wise or the features might not be suitable / have trade offs for other people).
Yes making data structures is important, and the reality of that is, there are people in the ecosystem creating fancy ones which can be leveraged for your use case.
If that doesn't exist then yea you have to write them. Sometimes that's difficult(you need to use unsafe), sometimes it's easyish and you can use all safe(I did this for a graph type). It can be done(lots of people are doing it), but I think what it shows is, data structures can be difficult to do correctly.
In a worst case scenario you could write it in asm inside rust if you really need a low level control, or write it in C/unsafe rust and ffi or just write it in.
Basically worst case scenario in rust is writing something closer to C.
That isn't to say a narrow ecosystem is necessarily bad, it can often be good if a particular language is used for a specific domain as all the libraries and data structures will likely be a better fit for your problems. Going outside of those constraints can often be very punishing in those languages though.
My advice would be not to judge any language on how easy it is to implement a doubly linked list. 99% of code you write will likely not be that, and that particular data structure exposes a lot of choices and trade offs at a time when youd be better served learning other parts of the language.
IMHO Rust's lifetime analysis should consider borrows only at the point of dereference, not just whenever you encounter an & symbol. They already do that with raw pointers - you can have as many pointers as you want but you only need to mark `unsafe` if you actually dereference one. So at least someone on the team knows how to make that work functionally.