Safety: A comparaison between Rust, C++ and Go

https://nested.substack.com/p/safety

by ephesee • 4 years ago

113 182 4 years ago

nested.substack.com

benreesman28• 4 years ago

Rust has a lot of great qualities that C++ lacks, but comparing `rustc` to `gcc` or `clang` on move-semantics checking is just kind of silly these days. `rustc` has `clang-tidy` built in.

`clang-tidy` is not letting you mutate or even access that moved-from "suffix" object without throwing an error.

It's annoying that you need `clang-tidy` and ASAN and shit to get comparable runtime safety even in greenfield C++, but that's not why to prefer Rust.

Prefer Rust because of a better traits system and pattern matching and syntax for `Maybe/Either` and a consistent build/library story and a number of other things.

blakehawkins• 4 years ago

And way, way better compiler errors thanks to a sane generics system

benreesman28• 4 years ago

And much better compiler errors. `rustc` about leads the pack on error messages of all the languages I use regularly.

bbojan• 4 years ago

I think you meant thanks to a sane(r) macro system? Both Rust and C++ use monomorphisation for generics, I believe shitty compiler errors are due to C++'s templating.

estebank9• 4 years ago

Your point is a fair one, but defaults matter. There's little reason for clang-tidy not to be part of the default clang invocation by now, other than an aversion to producing new output for existing projects (that you could argue are already "broken"). Unless clang-tidy has false positives, in which case the comparison isn't apples to apples then.

dataflow5• 4 years ago

Unless clang-tidy has false positives, in which case the comparison isn't apples to apples then.

Confused... so you're suggesting Rust's checks are somehow free of false positives? Doesn't the halting problem get in the way? One Rust-specific example: https://www.reddit.com/r/rust/comments/nr7a33/is_the_borrow_...

benreesman28• 4 years ago

Oh I completely agree that defaults matter, and I wouldn't advise anyone to go start some big C++ project unless they had a very good reason to.

But Rust vs. C++ is not an apples-to-apples comparison in this regard: Rust got a clean slate and was willing to cut ties with engineer-millenia of existing high-value software to do it.

In a perfect world Rust wouldn't be ambivalent at best and hostile at worst to C++ interop, c'est la vie.

pjmlp9• 4 years ago

They do, that is why any C++ shop where code quality is relevant has a DevOps team that cares about the right defaults being enforced on th CI/CD pipeline.

Devs that don't care only get to build on their own computers.

It isn't fullproof, but definitely helps to tame some cowboys.

arinlen2• 4 years ago

Your point is a fair one, but defaults matter.

This sort of comment is far from fair and misses the whole point.

The thesis of this article is how programming languages compare with regards to safety.

It makes no sense at all to compare particular implementations and try to pass personal assertions on particular features of said implementations as broad assertions about the programming languages they support.

So a particular Rust implementation is bundled with a linter. That's pretty convenient.

It just so happens that the linter is provided by a compiler stack that is also one of the main reference implementations of C++, and said linter also supports C++.

Is it fair to thus claim Rust is somehow superior to C++ just because a particular implementation enables by default it's linter on Rust code but not C++?

There's little reason for clang-tidy not to be part of the default clang invocation by now

It's perfectly fine that anyone forms their own personal opinion on what defaults a tool should ship with.

That says anything nothing about the programming languages and their safety though.

blub• 4 years ago

Objectively speaking, Rust does not "have a lot of great qualities that C++ lacks". Any new feature or improvement has its pluses, but also its minuses.

* Rust has traits, but does not support OOP. Architectures where OOP is particularly effective are proving to be a significant challenge for Rust - GUIs are the obvious one, but also game development Rust projects have to invent new approaches.

* Option/Result make the code flow obvious, but having to return them in nearly all function calls is tedious. Rust has had several attempts at alleviating this problem, but still hasn't matched the convenience of exceptions.

* match is IMO syntactic sugar and its benefits for correctness are being oversold. The fact that one is basically obliged to use it leads to code that's sometimes too deep. Exceptions would cut through this error-handling noise, if they were available.

* The build story is convenient, but this had the unintended effect of encouraging dependency explosion. Adding typical crates results in dozens of transitive dependencies being included in a project.

The notable improvement that Rust brings to the table is machine-verified memory safety with C++-like performance, but that of course comes at the cost of having to adapt code to what the borrow checker understands. If one needs the feature, then the cost is worth paying, if not, Rust is more of a personal choice than an inevitable conclusion.

And finally, perhaps Rust's biggest sin is that it's big, it's complex and there's no end in sight to the complexity spiral, just like for C++. I can only imagine the chagrin of the Rust community as they see themselves competing with Go for many projects where performance is not absolutely critical and often being second choice exactly because of this complexity.

ncmncm15• 4 years ago

More to the point, Rust lacks key features I need to capture essential semantics into libraries. So, the libraries I could write in Rust would be less powerful than libraries I can write in C++.

Among common uses for these more powerful features is to make misuse of the library into a compile-time error. Coding the library in Rust, if possible at all, would mean failing to prevent these usage errors.

The point here is that C++ puts more power in the hands of a library writer, and both the responsibility and capability to enforce safety in uses of the library. Rust jealously reserves maintaining safety to the compiler alone.

RobertWHurst• 4 years ago

To say the rust has a built in linter is wrong. A rust program that does not build because of a memory ownership error on the part of the programmer isn't rejected by the compiler due to a detected pattern, it is rejected because the program is "unsolvable" and cannot be built. I think a lot of people miss how integral the memory semantics Ruct enforces are to how it parses and compiles programs. If these things were simply lints it could be reasoned that a program could be built without following these semantics, that If you could simply go into the compilers source you could just turn them off/remove them. You can't. The way rust's compiler tracks memory is fundamental to how it compiles the binary. It is not simply pattern matching code or ast. Rust's compiler is actually tracking the lifecycle of every bit of memory allocated so it knows when to free it, and it does this at compile time without running the program. These memory semantics errors exist because they are integral. Turning them off would simply result in a broken compiler, or a program with no freeing of memory because the compile time reference counting rust implements becomes impossible.

jiehong• 4 years ago

Java falls a bit in between Go and Rust on that example:

Closures only allow variables that are effectively final, aka you can’t reassign them (the compiler will stop you).

But you could pass an object and update its internal state.

qsort2• 4 years ago

"final" in Java is kind of useless, really. A const mechanism like C++ has would go a long way and would be a perfect fit for the OO nature of the language.

eganjs• 4 years ago

Final in Java means the value of a variable, property or parameter will not change after its initial assignment. Values in Java can be either a reference to an object or a primitive such as an integer, double or bool. It's definitely far from useless as it asserts that the reference or value you capture in a closure is not an old version that has been replaced, this approach is a consequence of Java disallowing arbitrary pointers. IMO Java's biggest mistake here is mutability by default, which Kotlin has learned from. If you understand why it is this way it makes a lot of sense and tbh I think it promotes better code. That said I would like to see more immutability in Java and with things like Record classes you can see Java is moving in the right direction.

wruza3• 4 years ago

comparaison

Probableur a typeaux?

rob74• 4 years ago

Was this posted by a French speaker? Because in English it's "comparison", not "comparaison"...

ncmncm15• 4 years ago

Disingenuous.

The bad C++ code is in the very first line of the "make_appender" definition: capturing the closure's environment by reference is nonsense: It is equivalent to returning a reference to an argument. It is not, then, a closure at all.

Using a correctly-defined make_appender would not, then, produce undefined behavior when you use it, with or without "move".

What the author has done here was to take a too-obviously wrong operation, returning a reference to an argument, but dress it up with syntax that will look less familiar to some readers, and pass it off as insightful.

But using a wrong function and getting wrong results is not surprising.

Piling on more uses after, that give more wrong results, does not reveal anything more.

When you need disingenuous arguments to make your point, it tells us more about your point than about the thing you are trying to make a point about. And, publishing anyway tells us more about you.

Returning that fake closure should evoke a compiler warning, if you turn on warnings.

benreesman28• 4 years ago

I was trying to be a little more diplomatic in my sibling reply because I've locked horns with the Rust community before and not enjoyed it, but you're not wrong.

roca• 4 years ago

A function returning a value that depends on the lifetime of the function's parameter is not crazy at all. Every class getter method that returns a reference to a member of the class does this.

benreesman28• 4 years ago

Sure. But returning the address of a stack-allocated object is (usually) broken.

There isn't a right and wrong here: sometimes you want to opt in to the check for that, sometimes you want to opt out of it.

Sometimes I actually do want to fuck with addresses on the stack in weird, potentially architecture-dependent ways, it's rare but it happens.

I happen to think that Rust's linear/affine typing is by far the most usable low/zero-cost memory management model that anyone has demonstrated at scale and a real achievement in practical computer science, but it comes at a pretty serious cost in `Box`-this and `Arc`-that and `Rc`-other-thing and generally the borrow-checker being a PITA about some stuff we're used to doing.

Rust is very cool and I use it, but the "using C/C++ is fucking strangers without protection"-vibe got old years ago.

ncmncm15• 4 years ago

Hint: getters are code smell.

Getters that return references are code stink.

dataflow5• 4 years ago

You can add [[clang::lifetimebound]] on the suffix parameter and you get

  <source>:21:35: warning: temporary whose address is used as value of local variable 'append34' will be destroyed at the end of the full-expression [-Wdangling]
    auto append34 = make_appender({3, 4});

pfultz22• 4 years ago

You dont need annotations, cppcheck already warns with:

    test.cpp:16:45: error: Using object that is a temporary. [danglingTemporaryLifetime]
        assert((std::vector<int>{1, 2, 3, 4} == append34({1, 2}))); // FAIL: UB
                                                ^
    test.cpp:3:12: note: Return lambda.
        return [&](std::vector<int>&& items) {
               ^
    test.cpp:2:50: note: Passed to reference.
    auto make_appender(std::vector<int> const& suffix) {
                                                     ^
    test.cpp:4:36: note: Lambda captures variable by reference here.
            return append(move(items), suffix);
                                       ^
    test.cpp:15:35: note: Passed to 'make_appender'.
        auto append34 = make_appender({3, 4});
                                      ^
    test.cpp:15:35: note: Temporary created here.
        auto append34 = make_appender({3, 4});
                                      ^
    test.cpp:16:45: note: Using object that is a temporary.
        assert((std::vector<int>{1, 2, 3, 4} == append34({1, 2}))); // FAIL: UB

dannymi5• 4 years ago

The bad C++ code is in the very first line of the "make_appender" definition: capturing the closure's environment by reference is nonsense: It is equivalent to returning a reference to an argument.

If it is so bad, it should (in the sense of how things would be in an ideal world) not compile.

It is not, then, a closure at all.

It is a closure because all variables are closed-over and there are no free variables in the lambda body anymore. That is the definition of closure.

But using a wrong function and getting wrong results is not surprising.

In an ideal world, there should be a compilation error. (There is in Rust)

The majority of what's wrong in C++ is that it lets you do nonsensical (even dangerous) things, most of the time without even a warning (and not because it's technically impossible to warn--it just didn't occur to them). It's okay to acknowledge that--it's a product of its time.

Returning that fake closure should evoke a compiler warning, if you turn on warnings.

That "should" tells me all I need to know. In the end either safety is important, or it isn't. Choose accordingly.

jstimpfle3• 4 years ago

> In the end either safety is either important, or it isn't. Choose accordingly.

Not to disagree with your post but this comes across as very black-and-white.

keithalewis• 4 years ago

"Doctor, it hurts when I do that!"

unsafecast5• 4 years ago

If it is so bad, it should (in the sense of how things would be in an ideal world) not compile.

Yes, C++ can be a bad solution to a lot of problems, and that's okay. Use rust if you need a machine guarantee for memory safety (or you just like the language), you can use Go if you just don't care about that at all and want the language to take care of it. But you can use C++ for non-critical software that needs to be fast (games come to mind). Rust can be too much of a mental overhead than it's worth for some.

That closure is just not a good example. Nobody would write this, because when writing C++ code you _do_ think about whether you want a reference or not. Sure, a lot of bugs can happen but this is not, in my opinion, one of them.

If you want to prove a point, prove it fairly.

Note: I don't use C++ anymore, and I don't like it very much for other reasons.

jstimpfle3• 4 years ago

    std::vector<int> suffix{3, 4};
    auto append34 = make_appender(suffix);  // Version 1: test will work

    auto append34 = make_appender({3, 4});  // Version 2: test will fail

I was in a mood to type the examples but I accidentally made Version 1 because I had started with the author's first example. I wondered where the problem was and couldn't find any (neither running nor reading the code) until I noticed the author had changed to Version 2.

The problem is "obvious" in hindsight but one of the problems with C++ is that it makes certain things too implicit/convenient. I get that references are a staple feature in C++ but it's not at all obvious from the calling location that Version 2 is a bug. To see that, you have to navigate to the callee (finding which might be hard enough alone without a very solid IDE), and make sure that it's not capturing the argument by reference or not doing anything unsafe there.

It's often a problem when a seemingly "value" argument is turned into actually a pointer-to argument at the callee. There are other languages that have this too, and I've never liked it.

As someone who doesn't regularly code in C++ but has a solid understanding of the basics, I wonder why C++ ever allowed to have a reference parameter be called with a temporary? To me it feels like "References have value syntax but pointer semantics BUT you should program like it had value semantics"? Which to me would be exactly a premature optimization that is looking for trouble.

benreesman28• 4 years ago

Again, this isn't a right/wrong thing. Rust moves by default (and a lot of people find "=" a weird pun for that), C++ copies by default and has rvalue-references and an explicit `std::move`.

If you want copy in your C++ lambda, you start it `[=](...) {...}`, if you want take a pointer in your C++ lambda, you start it `[&](...) {...}`, if you want something trickier you do trickier stuff.

Rust opts you in to the nitpicky static analyzer and you have to opt out with `unsafe`, in C++ you have to opt in with e.g. `clang-tidy` or some annotations.

They are remarkably similar, just with different defaults.

snovv_crash• 4 years ago

You can also 'const' your std::vector when you declare it and it won't work. Any linter or having warnings turned on will catch these issues.

CrendKing• 4 years ago

The fact that you may know that make_appender definition being bad does not mean every C++ user knows as well. It's also impossible for you to know ALL the possible bad, UB leading C++ code out there.

I think the point the author tries to make is that, while C++ and Rust are probably "the same" for the most skillful and disciplined programmers (such as you), for average human, Rust just catches way more errors they make for them early. An extreme analogy would be trying to climb Everest all by yourself vs with a professional guide.

benreesman28• 4 years ago

Not to disagree necessarily, but if you (give me a little rope) bucket languages that are hard to get past the compiler but more often correct when you do (Rust, Haskell), and languages where it's pretty easy to get something past the compiler and tweak it until it works well enough for your purposes (JS, C/C++), the tweak-it-until-it-kinda-works languages are fucking killing it on adoption.

ncmncm15• 4 years ago

Literally anybody can turn on warnings and heed the results.

crabbygrabby• 4 years ago

It's possible the author actually made this mistake, and because c++ is C++ they didn't realize why/how. Not a lot of programmers have a good handle on c++, maybe even most don't... Hence these other languages.

ncmncm15• 4 years ago

If the author deliberately chose to compile with warnings turned off, in order to present an example that would crash, then that tells us more about the author than about the point.

alrlroipsp• 4 years ago

Screenshot absolutely make me •¶Žš‰»‚¯

jayp1418• 4 years ago

What about comparing to Ada Programming Language?

vitus2• 4 years ago

I feel like a better comparison would be to use std::span (C++20) to mimic Rust's slice. Otherwise you might be tricked into thinking that adding

    // hey don't pass in a temporary
    auto make_appender(std::vector<int>&& suffix) = delete;

(which turns the provided code into a compiler error under both g++ and clang++) is adequate to prevent the immediate class of issues (namely, C++ allows const Foo& and Foo&& to bind to temporaries).

Meanwhile, it's really really easy to make std::span dangle:

    #include <cassert>
    #include <span>
    #include <utility>
    #include <vector>
    
    std::vector<int> append(std::vector<int>&& items, std::span<int> suffix) {
      items.insert(items.end(), suffix.begin(), suffix.end());
      return items;
    }
    
    auto make_appender(std::span<int> suffix) {
      return [=](std::vector<int>&& items) {
        return append(std::move(items), suffix);
      };
    }
    
    auto make_appender34() {
      std::vector<int> vec = {3, 4};
      return make_appender(vec);
    }
    
    int main() {
      auto append34 = make_appender34();
      assert((std::vector<int>{1, 2, 3, 4} == append34({1, 2})));
    }

ncmncm15• 4 years ago

That would just be another tendentious example. Nobody would write a make_appender that takes a span argument, because it makes no sense.

The point we should take away is that is actually hard to invent plausible examples of the failure that we are being told Rust would prevent.

vitus2• 4 years ago

Nobody would write a make_appender that takes a span argument, because it makes no sense.

I don't agree with that. If you can guarantee that the data pointed to by the span will outlive your appender, then it's safe. And if you don't actually want to transfer ownership or incur the overhead of a copy, and you don't care if your input is a vector or an array, then it's the correct abstraction.

Replace std::span with std::weak_ptr (or a raw pointer), and replace the closure with a class (e.g. a tree where each node has a weak pointer to its parent), and tell me again that nobody would ever write that code. It's fundamentally the same concept: if your ownership model isn't ironclad, or if any of your assumptions are ever violated, then you can run into use-after-free.

kcartlidge2• 4 years ago

Totally not the point of the article, and totally subjective I know, but to me the thing that jumps out is how much more readable the Go code is than the others.

deeptote• 4 years ago

This is the main reason that I use Go as my main language, and why many orgs are starting to adopt it: it's easy to read and jump into. I would argue, however, that it's very easy to create antipatterns and just general spaghetti code with Go. A language that's easy to be productive with != one that's also easy to maintain. Design and philosophy becomes very important with large codebases in the language.

source: consultant, seen some truly heinous Go monoliths.

bsaul• 4 years ago

There are definitely some ways to do bad designs in go, but i have the feeling it will be more immediately apparent what's wrong (or at least what part of the system needs rework). The reason being that there are no ways to obfsucate an awful design by wrapping it on mountains of generics programming and language sugar, making the whole thing a lot worse.

It's only my gut feeling, but does that match your experience ?

arriu• 4 years ago

I agree. However, my gut reaction was that the style of the go code was written differently than what I’d expect if asked to work off the rust version.

agent281• 4 years ago

Definitely subjective. I don't find some parts very readable. E.g., this line took my a minute to parse:

  append34 := func() func([]int) []int {

If I was going to rank the readability I would say:

1. Rust function bodies 2. Go code 3. Rust function signatures 4. C++ code

Which you could argue is me shifting the boundaries a bit, but sufficiently statically typed languages seem to develop two (or more) sublanguages. Global complexity definitely pushes Rust down peg.

andai• 4 years ago

I don't write Go but it might have something to do with this:

https://go.dev/blog/declaration-syntax

Go's type syntax is unusual but supposedly much clearer when things get more involved.

hkalbasi• 4 years ago

Can you mention the difference that made Go code is more readable than C++ and Rust?

kcartlidge2• 4 years ago

Can you mention the difference that made Go code is more readable than C++ and Rust?

Probably not, and to be fair anyone else's preference is equally valid. I think largely what individuals consider most readable depends less on what's being read and assessed now, and more on what route a developer has taken to reach this point in their career.

If I'm honest it's more about unconscious familiarity with idioms and constructs than it is an isolated unbiased opinion.

And I'd probably also change my comment slightly to say that by "Go code" I really did mean the actual code doing the work; I find the tests far less appealing.

DmitryOlshansky• 4 years ago

The fact that the GC “owns” all of the memory happens to help a lot with lock-free stuff.

jeffbee• 4 years ago

There's a solid argument in here but it feels like there must be a better example. Can we think of a function that does something worth doing, in a way that programmers of all these languages would actually use, and that sets a subtle trap for C++ programmers? When I read this article all I see is a useless function that contains a completely obvious trap which, yes, Rust prevents, but also just thinking at all would have prevented.

Another small thing: the C++ in this article looks weird to C++ programmers because it qualified vector with std, but does not qualify move.

TinkersW2• 4 years ago

This would be a better article if the UB in the C++ example wasn't blindingly obvious-- no C++ programmer worth a damn would ever write this.

jrajav• 4 years ago

Why is this such a common defense for the peculiarities of C++? I see it pop up at least a couple of times, anytime C++ is criticized.

I don't have anything against taking pride in one's skill and craftsmanship, but excusing a tool's failings purely on the basis that one needs more skill to wield it and avoid those failings? I want to have that same level of skill and have my tool multiply my skill's output to the max, not have my skill wasted coaxing my tool to perform correctly.

If the implication is that the tool requiring more skill gives commensurate benefits, fair enough, but not if it's just hand-waving away obvious downsides.

TinkersW2• 4 years ago

Because the code in question isn't something a C++ dev would write, instead it looks like something someone who doesn't use the language much if at all, decided to use for this pretty silly comparison.

It would be one thing if this required skill, but this example is downright silly. Some other people here have posted more reasonable version, that might actually occur in the real world(like the example with std::span)

pfultz22• 4 years ago

Yea and C++ static analysis tools already warn for the case, so even for new C++ programmers where it might not be entirely obvious, its still easy to catch the error.

sagarm• 4 years ago

Yeah, agreed that a competent C++ dev would not write the code in the example. The charitable interpretation though is that errors of the same type can crop in real codebases, the example is just simplified for the purposes of discussion.

pornel• 4 years ago

In such examples you’re always primed to look for a mistake. It’s a different situation when you have 100K+ lines of code, a dozen developers, and a deadline.

It’s a difference between “look this is Wally” (duh, of course) and a game of “Where’s Wally?”.

Whenever a CVE is discussed people say that the error is obvious, and no good programmer would write like that. It’s easy in hindsight.

ncmncm15• 4 years ago

More to the point, the compiler warnings would save inexperienced programmers too.

phendrenad22• 4 years ago

Can we throw Python in too? Python has more safety than any of these languages, yet it's always left out of these discussions.

aliqot• 4 years ago

Is this satire?

pdimitar4• 4 years ago

You're joking, right? A dynamically-typed language has more safety?...

phendrenad22• 4 years ago

What is Python lacking that would make it as safe as Rust?

niekb• 4 years ago

The author could compile c++ with the sanitizers, i.e. -fsanitize=address,undefined and make a make_appender function that leverages perfect forwarding...:

  template<typename S>
  auto make_appender(S&& suffix)
  {
    return [perf_fwd_suffix = std::tuple{std::forward<S>(suffix)}](std::vector<int>&& items)
    {
        return append(std::move(items), std::get<0>(perf_fwd_suffix));
    };
  }

see: https://godbolt.org/z/M9P4MK4a8

Safety: A comparaison between Rust, C++ and Go

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