[Manishearth]

I'm interested in seeing your use cases where lifetime elision isn't helping. I've found that it's helpful in the vast majority of cases, and when it isn't working (for functions, at least) there's a decision to be made.

It also could be a programming style thing; I've seen newcomers from C++ often trying to program in the C++ style and having lifetime troubles because the C++ style isn't really amenable to Rust's model. (I feel this might be the issue since you mentioned "sometimes seemingly trivial" -- almost every time someone has said something like that about Rust it's a matter of a programming pattern not translating directly)

Also, really, lifetimes don't do away with the effort required in manual memory management, they just confer it to compile time, so at least you can be sure that your code works and will not break in the future. They're not really a new concept, you think about them anyway in C++, just in a different way.

[dave_ops]

I'm a functional programmer (Lisp, OCaml, Erlang), and I only touch C++ when I have to wrap it in something to interface with a higher-level language.

Most of the cases where I run into this problem and end up feeling like I didn't gain much, if anything, from doing a straight C implementation are situations with deeply nested data structures.

I get that the thinking is that the benefit is that once I've made the compiler stop complaining, my memory management model should at least be sound and safe, and that is a win. Though immediately following that I start to have dream-like fantasies where this entire static analysis stage is simply bolted onto C instead of being a whole new language.

Afterall you can do some pretty impressive stuff with nothing but a pile of preprocessor macros (see Objective C).

[pcwalton]

> Most of the cases where I run into this problem and end up feeling like I didn't gain much, if anything, from doing a straight C implementation are situations with deeply nested data structures.

Your feeling doesn't line up with what has been observed in practice. Empirically, people do not get the memory management right in C. They mess up, again and again and again. In Rust, however, the compiler enforces that you get it right.

> Though immediately following that I start to have dream-like fantasies where this entire static analysis stage is simply bolted onto C instead of being a whole new language.

I don't think it's really possible to bolt Rust's semantics onto C. Too much will break: in particular C code is not written with inherited mutability, which is critical to Rust. You could maybe do something like the proposed lifetime stuff in C++, which still requires lots of annotation, enough to effectively be a whole new language.

Rust has a lot better ergonomics anyway.

> Afterall you can do some pretty impressive stuff with nothing but a pile of preprocessor macros (see Objective C).

Objective-C isn't "a pile of preprocessor macros", and it would be completely impossible to implement the lifetime system using the preprocessor.

[dave_ops]

The first versions of Objective-C were most definitely implemented as pre-processors to C compilation.

[pcwalton]

That's not the same as using the C preprocessor to implement the language.

[jbandela1]

At this year's CppCon Herb Sutter the chair of the ISO C++ committee addressed just this issue of lifetime safety. Here is a video of his talk and includes a demo of the upcoming static analysis tool that can do this with very minimal annotations https://m.youtube.com/watch?v=hEx5DNLWGgA

I remember thinking when watching the talk that this was a very bad day for Rust as C++ could now do most of what Rust was promising

[pcwalton]

The lifetime stuff in C++ is full of annotations, with effectively just as many required as Rust. I think of it effectively as a separate language. It's also significantly more complex, with points-to analysis instead of inherited mutability, and the restrictions on pointer aliasing on function entry seem very restrictive compared to what RefCell provides.

I think that Rust's system has proven itself to be about as simple and easy to use as you can get in this space. I also think that you cannot just "bolt on" a lifetime system to an existing language that was not designed for it without large amounts of annotation, modification of existing code, and additional learning curve.

[pjmlp]

The danger here to Rust is the usual "worse is better".

OS vendors will happily just add GSL and static analysis driven support to C++, with Rust becoming the language that drove them to do that and that is it.

Microsoft (GSL + static analysis, C++/CX, System C#, .NET Native) and Apple (Swift) are already working on what might be their next systems programming language.

They might lack full Rust like safety, but they are a good enough incremental approach to safety, come with integration with their existing tools and libraries.

Which leaves Rust adoption for systems programming to other OS vendors, e.g. embedded space or open source OSes.

Remember, languages are a tiny portion of the whole eco-system. Tools, libraries and community play a bigger role.

[jbandela1]

I agree. We are not starting out with a blank slate. There are already billions of lines of C++ in mission-critical production use. Companies such a Microsoft, Apple, Google, and Facebook run on C++. In addition, it has vendor support on all the major operating systems. In contrast, not even Mozilla, has bet the company on Rust (Servo is experimental and Mozilla has made no promises of actually integrating it into Firefox.) Also, Rust is not vendor supported on any platform.

So if you are a CTO or someone who has the responsibility of deciding what language to use for your performance critical software, you already have a large bias toward C++. You may be swayed toward Rust by the fact that Rust is memory safe. However, when someone comes and tells you that with this open source tool for C++ backed by the big names in C++, and developed and supported by Microsoft, and just by using the GSL types you can get most of the benefit of Rust, you will decide that the delta of improvement of Rust over C++ is not worth it.

TLDR: In programming language use pragmatic considerations trump purity. Multibillion dollar companies run on C++. With GSL and static analysis, C++ is "good enough".

[pcwalton]

That is very '90s, pre-programming-language-Renaissance thinking. If that thinking actually dominated, then you would never have seen the rise of Python, Ruby, Go, Node, Perl, PHP, Scala, Clojure, and so forth during the 2000s and 2010s. During the '90s, people predicted that Java would be the last programming language that anyone would ever use, using the same kinds of reasoning. That turned out to be false.

> You may be swayed toward Rust by the fact that Rust is memory safe. However, when someone comes and tells you that with this open source tool for C++ backed by the big names in C++, and developed and supported by Microsoft, and just by using the GSL types you can get most of the benefit of Rust, you will decide that the delta of improvement of Rust over C++ is not worth it.

Replace "Rust" with "Ruby on Rails", "C++" with "Java", and "GSL types" with "Spring", and you could make the same statement in 2005. It might even sound plausible. It would also be an incredibly wrong prediction.

> There are already billions of lines of C++ in mission-critical production use.

How many lines of memory-safe C++ are there in production use? The amount of memory-safe Rust code far exceeds that.

Ergonomics and the ecosystem matter. The fact is that the proposed static analysis tool for C++ is very restrictive and complex, from everything I've seen so far, and coupled with the annotation burden equal to that of Rust effectively makes it into a completely different language.

[tatterdemalion]

I agree that this might be a reason that people delay adoption, but I think things will change when the people who adopt Rust do better than the people who don't. This is similar to how things changed when people who adopted scripting languages for their web apps did better than people who didn't.

[Manishearth]

> Mozilla has made no promises of actually integrating it into Firefox.

Rust is already being integrated into Firefox

[jguegant]

Exactly! No matter the future of Rust, it has already shaken the programming community and motivated the other language designers to catch up in that domain.

As to guess whether Rust will put down C++ forever and ever, is another hard question. It will be a matter of community and sadly money... For instance, Apple's already got a much better market share with Swift (look at the job trends) simply because it's Apple. Same goes for JavaScript greatly helped by Google (V8) for their interest (a faster JavaScript engine ==> better usage of Google's web services).

[pcwalton]

> Microsoft (GSL + static analysis, C++/CX, System C#, .NET Native) and Apple (Swift) are already working on what might be their next systems programming language.

Swift at least isn't in the same space as Rust. It's a fully garbage-collected language.

> Remember, languages are a tiny portion of the whole eco-system. Tools, libraries and community play a bigger role.

And Rust has the most memory-safe low-level systems code available today. It also has Cargo and crates.io, which allow that code to be easily reused.

By contrast, existing C++ code isn't safe C++ code. It will have to be ported, often by drastically altering the idioms in use, and that takes a lot of time.

[pjmlp]

> Swift at least isn't in the same space as Rust. It's a fully garbage-collected language.

Have you spent any time reading Apple documentation?

https://developer.apple.com/swift/

"Swift is a successor to both the C and Objective-C languages."

Mesa/Cedar at Xerox PARC was also systems programming language with RC.

Going back to my comment "Remember, languages are a tiny portion of the whole eco-system. Tools, libraries and community play a bigger role.".

<devil advocate mode>

Give me Swift like Playground, Instruments integration, XCode and LLDB integration. Ability to call any Mac API the same way Swift does. Then maybe our customers will request Rust for our iDevices projects.

Give me Visual Studio integration, ability to define WinRT controls like C++/CX, create and debug COM like VC++, mixed mode debugging with .NET. Then maybe our customers will request Rust for our Windows projects.

</devil advocate mode>

Again, I am pretty aware that Rust is way better than half baked solutions like GSL + static analysis, but I have quite a few grey hairs already.

My first C++ compiler was Turbo C++ 1.0 for MS-DOS, remember when it was just released?

I also remember when C had zero presence on home computers.

Which means I was there when Ada, Modula-2, Modula-3, Oberon and derivatives were steam rolled by OS vendors betting the house in C.

As an early C++ adopter, I also carry quite a few flame war scars from being on the C++ side of the fence back on those days (vs C). As I always advocated for the C++ improved safety over what C offers.

> And Rust has the most memory-safe low-level systems code available today.

I agree, but do the OS vendors that sell the SDKs we are allowed to use, also agree or will hide their head on the sand and do another round of "worse is better" with their tools?

> By contrast, existing C++ code isn't safe C++ code. It will have to be ported, often by drastically altering the idioms in use, and that takes a lot of time.

Yes, but the eco-system is already here. Which means most companies will rather endure a slow Python 2 to Python 3 code re-factoring than move to another language.

I really want Rust to succeed and be the language I can use whenever I have to go outside JVM, .NET and mobile worlds.

However I have seen too many nice languages become victim of "worse is better" syndrome.

So sorry if my type of "heads up comment" isn't welcome.

[steveklabnik]

While I'm glad to see C++ improve, and I'm happy that Rust seemed to influence this, I don't think that it will kill either Rust or C++.

As you say, there's a ton of C++ code out there. However, five things:

  1. A _lot_ of that is C++98.
  2. These rules are just proposed. There's tons of time.
  3. They don't give you as much safety as Rust.
  4. Many people have already rejected C++.
  5. Langauges don't die.

So, one and two are kind of related. We're still in the "propose" stage for all of this, which means there are still years before this would make its way into the standard. How long have things like modules taken? Who knows when the rules will be final, and when they'll actually land. You get all of this (and more) in Rust right now.

As for three, while these rules help, and are laudable, they still don't give you data race freedom. In general, they're not intended to be an ironclad safety system, just something to help catch more cases where something went wrong. See Herb's insistence that pointers should be able to dangle in some circumstances, as an example. I saw a comment on Reddit that straddles three and four, here it is: https://www.reddit.com/r/programming/comments/3m6j2c/cppcon_...

   > Just follow this set of hundreds of rules (seriously, go read the core
   > guidelines), ignore 20 years of material written about C++ before the
   > year 2011, use this non-standard third-party library of stuff we
   > really like, and you too can have a fraction of Rust's compile safety.

This is phrased a little to sarcastically imho, but there's a nugget of truth there. One of C++'s problems is that it's just got too many features, bolted on over decades. Is bolting on yet another feature the way forward? How much of that existing C++ code will even be able to take advantage of these new safety features?

A lot of people have already rejected C++, for various reasons. The details of those reasons are varied, and may be good reasons or bad reasons, but the point is, they've already said nope. A lot of people coming to Rust fit in this category. "I tried C++ one time, but it's too complex." "I can write some basic C++, but I'm not confident my code is correct." "I write Ruby code, C++ looks terrifying, and I hear it's hard never tried it." And so on. Our industry is huge, there are a lot of developers, and not all of them will use a single language even if it's 'better.' That cuts both ways.

And ties into five. I don't think the question "Will Rust kill C++" is well formed. A language that's used as much as C++ is will never die. We'll have C++ code in production for at least my lifetime, I'd bet. Rust doesn't need for C++ to go away. Languages aren't the Highlander, there can (and often are) more than one. I mean, look at Python and Ruby. They're really similar languages from a PLT perspective, but they're both active, healthy, used-by-millions languages, and many of their programmers wouldn't switch to the other. This is totally fine.

[pjmlp]

I hope that Rust succeeds in the mainstream.

If anything, please take my point of view of someone that cannot ever use Rust until the customers say I am allowed to.

On my type of work we only use first class languages, those that are provided as part of whatever platform we are targeting.

This is my point of view of "worse is better".

Many might have rejected C++ or C (e.g. I don't like C at all), but many more are on the same boat as I.

For us system programming means C++ and C, until the IT department or customer allows anything else on our dev machines.

[Manishearth]

IMO "kill C++" is better replaced with "Will Rust or isocppcore be the language of choice for new C++ codebases". Where "new" includes dependencies (i.e. a project heavily dependent on an in-house C++ library used elsewhere doesn't ocunt)

I think in the majority of cases this might turn out to happen.

[weinzierl]

Also Rust has the freedom to just leave dangerous features out of the language [1]. This is something we will never be able to do with C++ without transforming it in a not backwards compatible manner.

And it's not only about safety: a language that doesn't suffer from the consequences of legacy design choices is just less mental burden, easier to learn and easier to teach.

[1] http://graydon2.dreamwidth.org/218040.html

[jguegant]

One can simply ditch the C++ backward compatible features into an "unsafe" part of C++. That's exactly what the talk given by Herb at the CppConf is trying to address. All the old unsafe part of C++ will trigger errors or warnings. But if truly necessary one will be able to disable these protections!

[pcwalton]

> All the old unsafe part of C++ will trigger errors or warnings.

And by breaking backwards compatibility so heavily, it effectively makes the new safe C++ into a different language.

[jbandela1]

I was at the presentations, and basically other than owner<T>, and [[suppress]] I do not remember other annotations. In fact, Herb made a point that having too many anotations was a weakness of Rust, and that they wanted to not have those annotations. There were some types to use such as array_view, string_view etc, but not annotations. Perhaps you are thinking of Herb's slides where he shows things like _In_reads_(num). Those are not part of GSL. He was just contrasting the annotation heavy way Microsoft does static analysis now, with the GSL which does not have these annotations.

[pcwalton]

I'm referring mainly to [[lifetime(this)]] and friends. Those correspond directly to the lifetime annotations in Rust. Read the paper for more details.

> In fact, Herb made a point that having too many anotations was a weakness of Rust, and that they wanted to not have those annotations.

That's because Herb didn't understand Rust.

> Perhaps you are thinking of Herb's slides where he shows things like _In_reads_(num). Those are not part of GSL.

No, I'm referring to the annotations I saw in the paper: https://github.com/isocpp/CppCoreGuidelines/blob/master/docs...

[steveklabnik]

  >  Herb made a point that having too many anotations was a weakness of Rust,

While he did say that, some other comments of his made it sound like he had checked out older Rust, without elision and with pointer sigils and stuff.

[Manishearth]

Check out the actual paper on the isocpp github repo. There are `[[lifetime(foo)]]` annotations.

Their proposal does include more elision than Rust (which actually leads to a loss of expressivity of patterns that arise in complex systems), but they still have plenty of annotations.

[Manishearth]

Functional idioms don't translate cleanly either :)

If you're using Rust for FFI from functional languages (or any language, really) you need to use a fair amount of unsafe code to get the interface correctly. There's not much benefit for simple things (aside from cases like these: https://gist.github.com/steveklabnik/1a3ec0ca676aaddf766e), but for more complex things it works out pretty nicely.