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> I struggle to believe that C or C++ can be written safely

It can. You just need to avoid those performance optimizations that were en vogue in the 90s/early00s. Luckily modern computers (and the more modern C++ standards) can handle value semantics just fine and you don't need to put pointers into vectors anymore because directly putting the data there would be too costly, etc.

If you only use the new (C++11 up) smart pointers (avoiding new/delete) you've essentially achieved 80% of Rust's safety model. Add rigorous application of const correctness and you're good to go. Rust still adds a few important things but until its eco system is matured (and there is real tooling) modern C++ is a pretty good alternative.

As an analogy, you can write safe code in assembler as well if you and your team are incredibly disciplined and only interact with libraries written with a similar amount of discipline. The appeal of alternatives is you can write safe code with a fraction of the discipline and mental effort required.

There is no extra “discipline“ or “mental effort” required to write safe C++. Don’t use new/delete/free/malloc and don’t use operator&. Of course, you can say that we might as well remove them from the language entirely, but I really don’t think it takes extra effort not to use them.

There are countless ways of causing undefined behaviour in C++ (not including memory management mistakes) as well as platform specific behaviour that you don't see in other languages. It's a very complex language to master compared to alternatives.

See eg http://blog.regehr.org/archives/140

C++14:

  auto p = std::make_unique<int>(5);
  auto q = std::move(p);
  std::cout << *p << std::endl;

Segfault using the “safe” C++ features. I'm a fan of modern C++, but it's not safe (in a Rust sense) even if you stick to C++11/C++14 features.

For comparison, the same thing in Rust:

  fn main() {
      let p = Box::new(5);
      let q = p;
      println!("{}", p);
  }

gives, upon compiling:

    error: use of moved value: `p` [E0382]
    println!("{}", p);
                   ^
    note: in this expansion of format_args!
    note: in this expansion of print! (defined in <std macros>)
    note: in this expansion of println! (defined in <std macros>)
    help: run `rustc --explain E0382` to see a detailed explanation
    note: `p` moved here because it has type `Box<i32>`, which is moved
    by default
    let q = p;
        ^
    help: if you would like to borrow the value instead, use a `ref`
    binding as shown:
    let ref q = p;
    error: aborting due to previous error

Running `rustc --explain E0382` or going to https://doc.rust-lang.org/nightly/error-index.html#E0382 gives you an extended error message as well.

> As an SRE/SysAdmin I struggle to believe that C or C++ can be written safely.

It doesn’t make sense to talk about C and C++ together like that and the idea that it would possibly maybe make sense to talk about two fairly different languages the same way is very much the root cause why some people consider it impossible to write “safe” C++. C and C++ probably have as much in common as C and Rust (both of these have pointers, so they must be the same) or as Haskell and Java (both of these have types/classes, so they must be the same).

I knew I was going to get this comment when I wrote this...

I only mention those two together as the previous options for low level, no runtime languages. Outside of Rust both C and C++ were independent options I've considered investing more deeply in.

It does make sense to talk about C and C++ together like this. The fact is that writing high performance systems software means using systems interfaces, and until there is a portable interface that doesn't imply the use of malloc, pointers, etc., you can't escape the C legacy of C++ and the inherently unsafe product of it.

Wherever you look in the C/C++ world you find this legacy (POSIX, OpenGL, OpenMAX, OpenMP, OpenCL, on and on) so no matter how determined you are to try to match Rust with `safe' C++ you get dragged back into C. The term "C/C++" is used and understood because it is 100% appropriate, and it will continue to be appropriate as long as unsafe C/C++ interfaces proliferate.

Obviously Rust can't completely solve this problem either, but Rust at least provides a mechanism to isolate the C legacy parts behind tested and supposedly `safe' API interfaces, leaving the developer exclusively within his type+memory+data race safe environment. That is a superior model.

This is exactly the scenario I found so confusing, and why I wrote this. I can understand not wanting to use F# or Scala for sysadmin work, but OCaml or Haskell would give you the safely and 95% of the performance (i.e. much better than Python) without the need for manual memory management.

Did you consider either of those? Were your reasons for preferring Rust similar to what I put in the article?

I answered a similar question to a sibling comment but I think it boils down to, I didn't come to Rust for functional features but I definitely enjoy them. The languages you mention in the post have a much higher learning curve coming out of Python. I spent a few tries "learning" Haskell and I really didn't enjoy it. In general when I've looked at Scala/Haskell/F# they use so many multi-char operators that it starts to look like line noise. OCaml always felt a bit too niche for me too I think, though that may be bias of the industry I'm in.

It's important to note that F# doesn't really have many operators at all. The one most people see, |> which "pipes" an argument, is defined in an F# library, not in the compiler or part of the core language. You can define it yourself to be anything you like, or not use it at all. The language is unaware of it and treats it like anything else. The definition is just:

  let (|>) x f = f x

That's literally function application, in reverse. That's all. It comes in handy for type inference and to make things look nice, but isn't special in any way. I mention this as one comment as to why Rust doesn't have such an operator was that "Rust uses channels for data flow" which is a non-sequiter. Rust just doesn't value conciseness as much, and I'm guessing the safety/perf restrictions might complicate matters.

In fact, even the + and - operators are implemented in F# and shouldn't count as part of the language (just very commonly used bits of the stdlib). I fear that perhaps not enough intros to F# focus on the relatively simple underlying language, and that everything else on top is just an application of said language.

With the type system, it's actually easy to figure out the operators, based on the type alone. Looking at |> for instance, we see a type of:

  'a -> ('a -> 'b) -> 'b

This makes it entirely obvious. There's only one implementation for such a type definition. This holds true for so much of the stdlib that the "noise" quickly fades away. This is relevant as magic cannot hide, and misuse will quickly be identified by the compiler.

But it's a valuable comment as it illustrates that the simplicity is not being marketed correctly and turning away potential users.

By 95% of performance you are surely measuring throughput on a logarithmic scale or something? Haskell is great, but getting within C performance requires careful very careful Haskell writing at least.

Well of course but you need to know what you are doing in C as well. Isn't the point just, a lot of people do, as compared to Haskell? Granted, the C compilers make a difference, too.

Yes.

In Haskell you get correct by default and have to work for speed. In C your program is fast by default, but wrong, and you have to work for correctness.

One of the major reasons for being interested in Rust is that it is something that is much easier to convince coworkers of.

OCaml and Haskell have somewhat odd syntax, for someone who is coming from C like languages or even Python. You need to learn a bunch of functional programming concepts to use them effectively. You are still limited in what you can do, such as writing a native extension module for your existing Python code base. And they don't really help on one of the major selling points of Rust, which is to be able to write safe multi-threaded code with shared, mutable data structures. While there may be lots of good high-level parallelism available, at some point for certain problems you really just want to be able to use a shared, mutable data structure, but doing so in almost any language but Rust makes it very easy to make a mistake and have aliased, mutable references to it that can invalidate all of your logic, even if it isn't actually memory unsafe.

> I struggle to believe that C or C++ can be written safely

There's plenty of evidence it can, for certain values of "program". redis comes to mind as a product with a specific goal and implementation, and well managed design process that makes that happen.

The problem is when projects grow to have dozens of developers, of varying skill, pumping in features in a continual battle to stay up to date with standards - like a web browser. Then, I think the possibility of secure C is shown to approach 0.

But this whole time, if efficiency was your aim, why not use, say OCaml? But good viewpoint: Rust is actually friendly enough that it is viable for the kind of things you mention.

Another thing is the lack of runtime is really compelling. I can continue to write Python and can drop into Rust for hot code. Right now this is through C which does get me a bit of unsafety but it's much smaller scope. As Rust becomes more mature I'm looking forward to the ABI stabilizing so other languages can build ffi interfaces against it directly.

I'll admit that OCaml is something that I've looked at before but it didn't have the staying power for me. It's likely just because it was too different at the time compared to what I was used to.

C++11 aims to make those problems much less severe - but most software with such emergy patches probably started out long before then.

As to how much the newer features help, time will tell...

We should be seeing completely safe C++ code soon.

Take a look at Herb Sutter's CppCon talk this year:

https://www.youtube.com/watch?v=hEx5DNLWGgA

Reinventing the wheel isn't entirely necessary. Though if you're a SysAdmin and you write your codebase in Rust.. that's some nice job security. ;)

I'd already looked through the slides for that talk but I'll check out the video. Thanks!

I think C++ has a lot of awesome stuff coming out but I find Rust more pleasant to code in. Also having package/dependency management has been great compared to using the old versions of libraries that come with distros or tracking down all the transitive dependencies of software. Rust is just a more delightful experience out of the box.

> Though if you're a SysAdmin and you write your codebase in Rust.. that's some nice job security. ;)

I definitely understand this but I don't think it's true and will be less and less true over time. It is becoming very common in the SRE/SysAdmin industry that strong coding skills is a requirement. When I started 10 years ago that was very different but it's becoming harder and harder to find jobs as a Linux grunt. The SREs I work with care about software engineering best practices, code review, testing, continuous integration, etc.

Also, even if that were true, I'd much rather have people with a weaker understanding contribute to Rust where the compiler has your back. If you haven't used Rust you might be surprised how good the error messages are. Once you spend a bit of time understanding the basics the compiler is super helpful.

Once C++ allows people to flip a switch to produce guaranteed memory safe code, then it can start really comparing itself on that metric. (This would be fantastic. Think of the resources that'd be spent on such research! It'd be world-changing.) But even then, the inherent differences in a statement oriented vs expression oriented is likely to keep C++ being needlessly verbose.

And I object to using Rust (or other production-level but "edge" languages) as being "job security". If the underlying software matters enough that using Rust has significant benefits, then it matters enough that employees spend a few days learning a bit of Rust. This fear of languages as if learning a language was this huge mountain to scale in hiring is just silly. The actual code and environment probably outweighs the language used significantly.

The real exception to this is if you're running a codebase that has essentially non-programmers adding bits here and there. Somewhere where you know that the individual contributors will find learning a language to be a higher barrier than contributing new pieces of code. (So either a rather trivial system, or contributors that have an unusually low capacity.)

I think you mean employees spend half a year to know enough Rust to be comfortable. That's how long it took me and others on my team to learn Java at a level where we knew the idioms, patterns and enough of the libraries. All of us had significant experience in other OO programming langauges.

Learning a language in days is a fairytale, the fact that you're so cavalier about this point makes it seem that you're more interested in doing advocacy than having an honest discussion.

Take the amount of time that it takes to become comfortable in a given language, and now increase that by an order of magnitude: this is how long it will take you to become comfortable writing C++ unsupervised. The language simply has too many subtle footguns to allow a beginner to be unleashed on a codebase (compare Java, where the worst a beginner will do is write a tangled mess of inflexible classes, but it will still largely work). The massive quantities of pre-C++11 documentation out there aren't doing the language any good either. And colleges (with the exception of game development programs) aren't teaching C++ anymore (and where they are, they're teaching C++98/03), so writing anything new in C++ means you're either going to maintain this yourself in perpetuity (talk about job security), or you're going to commit to a long period of coaching a beginner on the language, or you're going to hire an experienced C++ programmer for a significant multiple of what a less specialized programmer would have cost you.

So in the context of a conversation about the costs of training and long-term maintainability, well, you should probably write all your stuff in Java, but if you can't, then you're better off selecting Rust over C++. I can teach Rust to anyone that knows Python, and once you know Rust you're at least familiar with the most useful subset of C++.

There are plenty of C++ programmers to hire from. I know because we are hiring both at experienced and junior levels. Furthermore, a C++ programmer is not significantly more expensive than other programmers according to SO salary surveys. An experienced programmer will demand a good salary no matter which language he uses.

I gather from this post that you seem to use a risky strategy for your development - let juniors loose on a problem and hope that Rust/Java will save them. Or is that just a straw man? In any case, all juniors should get coaching, CI with static analysis and code reviews are likewise highly recommended.

Finally, I can't understand how someone can recommend Rust over C++ for long-term maintainability with a straight face.

The first stable version of Rust was announced four months ago, let's talk again in 10 years and see how your code from 2015 is doing.

I've hired people to work on .net apps (C#) as well as hiring devs with no F# experience and this is simply not my experience at all. I hired someone to do a spike of a project in Rust, ditto. And just this last week I met with one of my consultants that just started using F# the week prior. His F# code isn't quite idiomatic but he's written ~1000 lines of usable code. I've personally investigated and made bugfixes to a system written in a language/platform in which I had no experience.

Therefore I think it's quite fine to say it takes a few days to learn a bit of a language, enough to start contributing. Enough that it's not "job security" to pick something that provides a real benefit.

Like I said somewhere, a safe subset of C++ sounds wonderful at first, but it also has demerits:

- If you enforce memory safety to all of your code, the number of the libraries that you can use will be severely limited. Imagine if you can only use C++14 libraries. How many C++14 libraries are out there? And I'm not sure if there will be many libraries written in safe C++, at least for the next few years. The adoption rate for newer C++ standards (C++11, C++14) was generally not satisfactory.

- If you only enforce memory safety to your own code, then you could use the existing ecosystem. But in that case, your program will still segfault because of the libraries you're using. Admittedly this is also a concern of Rust when you use C libraries in Rust. The more safe code you use, the safer your program is. The problem is, if you choose this route, there's not much ecosystem-ish advantage in the C++'s side. You will also have to "reinvent the wheel" as you would have to do in Rust.

This problem all boils to this: adding guaranteed memory safety to the unsafe language is a breaking change. And the problems occurred by breaking changes are very hard to solve.

Rereading your comment it feels like you've moved the goal posts and are being overly cynical. (This presentations essentially addressed your previous concern by providing interoperability between new safe code and existing code that doesn't have safety guarantees)

These are valid concerns, but you're being very dismissive of the benefits

I think confining errors to libraries is generally a good strategy. In effect you are guaranteeing that you're not going to introduce any new unsafe code.

It might uncover errors in the existing code.. but that's a much smaller issue and one that fades with time (esp if you're talking about libraries that a lot of people are using)

Is this "good enough" for a brand new aircraft-control/heart-lung-machine system? Maybe not. Maybe then you should start from the ground up using either Rust or C++/GSL entirely. But I think for most use cases this is sufficient and brings huge immediate benefits now. And of course with time libraries will be updated to include safety guarantees (which for the most part seem like it wouldn't involve a ton of work)

This is more of an organic process that basically in some form preserves the millions of man hours people have invested in C++ and less of a clean slate solution. As I've said before, you gotta make a living now in the current reality with the current codebases and the current tools. You can't just judge languages in a vaccuum.

> which for the most part seem like it wouldn't involve a ton of work

This is probably the reason why our opinions vary. I believe rewriting existing libraries to be safe would be a tremendous amount of work. This estimation comes from my experiences with Rust. Safety guarantee hugely affects the interfaces of the libraries. You cannot "just" gradually increase safety of your library. It is basically a redesign. At least with what Rust currently provides this was my experience. And the method suggested by Herb Sutter seems to be very similar to Rust's. So I expect the same churn to happen in the C++ ecosystem, and it would effectively split the ecosystem into two: safe ones and unsafe ones.

Let me rephrase myself again: if adding safety to C++ in a gradual manner was that easy, Rust would have not been invented in the first place. The Mozilla guys could just use C++. There's a reason why Rust had to exist, despite all the "reinventing the wheel".

I guess it's a matter of opinion but I think you're wrong that you have to redesign stuff. Most of the guarantees in essence already exist b/c of best-practices (like RIIA) - they're just not guaranteed by a validating program.

Don't diminish it, b/c the presented solution is non obvious/trivial. If it was, it would have been done ages ago.

So either A - The Mozilla folks may have not thought of this solution

B - At the time of Rust's development C++ was stagnant and not evolving as it is right now. There wasn't a lot of hope for fixing it at the time. It's thanks to the work of several people that the C++ standards committee now is a fast moving organization.

If Mozilla were considering starting the Rust project in 2016 I don't think they would have gone ahead with it