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Comment by CrendKing | Hacker News Reader

But Edition can exist only because Rust intrinsically has the concept of package, which naturally defines the boundary. C++ has nothing. How do you denote a.cpp be of cpp_2017 edition which b.cpp be cpp_2026? Some per-file comment line at top of each file?

C++ is a mess in that it has too much historic baggage while trying to adapt to a fiercely changing landscape. Like the article says, it has to make drastic changes to keep up, but such changes will probably kill 80% of its target audiences. I think putting C++ in maintenance mode and keep it as a "legacy" language is the way to go. It is time to either switch to Rust, or pick one of its successor languages and put effort into it.

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Rust doesn't have the concept of package. (Cargo does, but Cargo is a different thing from Rust, and it's entirely possible to use Rust without Cargo).

Rust has the concept of _crate_, which is very close to the concept of compilation unit in C++. You build a crate by invoking `rustc` with a particular set of arguments, just as you build a compilation unit by invoking `g++` or `clang++` with a particular set of arguments.

One of these arguments defines the edition, for Rust, just like it could for C++.

That only works for C++ code using C++20 modules (i.e. for approximately nothing). With textual includes, you need to be able to switch back and forth the edition within a single compilation unit.

Mixing editions in a file happens in Rust with the macro system. You write a macro to generate code in your edition and the generation happens in the callers crate, no matter what edition it is.

Modules are starting to come out. They have some growing pains, but they are now ready for early adopters and are looking like they will be good. I'm still in wait and see mode (I'm not an early adopter), but so far everything just looks like growing pains that will be solved and then they will take off.

At the current rate, we'll have full module support for all of the most popular C++ libraries sometime around Apr 7th, 2618.

https://arewemodulesyet.org/

I expect modules to follow a S curve of growth. Starting in about 2 years projects will start to adopt in mass, and over the next 5-10 years there will be fast growth and then (in about 12 years!) on a few stragglers will not use modules. They are not free to adopt but there appear to be a lot of long term savings from paying the price.

I'll mention that library maintainers/authors can't even _consider_ modules unless they set C++20 as a requirement. Many/most popular libraries will not do that anytime soon. I maintain a moderately-popular library and my requirement is C++11... now, to be fair, I started it back in 2016-2017; but still, I won't even consider requiring C++20 until C++17-and-earlier application code is close to disappearing.

It's not clear that modules alone will solve One Definition Rule issues that you're describing. It's actually more likely that programs will have different object files building against different Built Module Interfaces for the same module interface. Especially for widely used modules like the standard std one.

But! We'll be able to see all the extra parsing happen so in theory you could track down the incompatibilities and do something about them.

> I think putting C++ in maintenance mode and keep it as a "legacy" language is the way to go

I agree but also understand this is absolutely wishful thinking. There is so much inertia and natural resistance to change that C++ will be around for the next century barring nuclear armageddon.

Cobol's still around. Just because a language exists doesn't mean that we have to keep releasing updated specifications and compiler versions rather than moving all those resources to better languages.

COBOL's most recent standard was released in 2023, which rather ruins your point.

I think the existence of COBOL-2023 actually suggests that it's not merely possible that in effect C++ 26 is the last C++ but that maybe C++ 17 was (in the same sense) already the last C++ and we just didn't know it.

After all doubtless COBOL's proponents did not regard COBOL-85 as the last COBOL - from their point of view COBOL-2002 was just a somewhat delayed further revision of the language that people had previously overlooked, surely now things were back on track. But in practice yeah, by the time of COBOL-2002 that's a dead language.

Fully agree, because for the use cases of being a safer C, and keeping stuff like LLVM and GCC running, that is already good enough.

From my point of view C++26 is going to be the last one that actually matters, because too many are looking forward to whatever reflection support it can provide, otherwise that would be C++23.

There is also the whole issue that past C++17, all compilers seem like a swiss cheese in language support for the two following language revisions.

I don't think even that would suffice. :)

> I think putting C++ in maintenance mode and keep it as a "legacy" language is the way to go

That is not possible. The the following function in C++ std::vector<something> doSomething(std::string); Simple enough, memory safe (at least the interface, who knows what happens inside), performant, but how do you call that function from anything else? If you want to use anything else with C++ it needs to speak C++ and the means vector and string needs to interoperate.

You can interoperate via C ABI and just not use the C++ standard types across modules - which is the sane thing to do. Every other language that supports FFI via C linkage does this, only C++ insists on this craziness.

Also I wouldn't start by rewriting the thing that calls do_something, I'd start by rewriting do_something. Calling into rust from c++ using something like zngur lets you define rust types in c++ and then call idiomatic rust. You can't do it in the opposite direction because you cannot safely represent all c++ types in rust, because some of them aren't safe.

I have millions of lines of C++. do_something exists and is used but a lot of those lines and works well. I have a new feature that needs to call do_something. I'm not rewriting any code. My current code base was a rewrite of previous code into C++ started before rust existed), and it costs a nearly a billion dollars! I cannot go to my bosses and say that expensive rewrite that is only now starting to pay off because of how much better our code is needs to be scrapped. Maybe in 20 years we can ask for another billion (adjust for inflation) to rewrite again, but today either I write C++, or I interoperate with existing C++ with minimal effort.

I'm working on interoperation with existing C++. It is a hard problem and so far every answer I've found means all of our new features still needs to be written in C++ but now I'm putting in a framework where that code could be used by non-C++. I hope in 5 years that framework is in place by enough that early adopters can write something other than C++ - only time will tell though.

Yeah that use case is harder, but I'm involved in a similar one. Our approach is to split off new work as a separate process when possible and do it entirely in rust. You can call into c++ from rust, it just means more unsafe code in rust wrapping the c++ that has to change when you or your great grandchild finally do get around to writing do_something in rust. I am super aware of how daunting it is, especially if your customer base isn't advocating for the switch. Which most don't care until they get pwned and then they come with lawyers. Autocxx has proven a painful way to go. The chrome team has had some input to stuff and seem to be making it better.

Sure I can do that - but my example C++ function is fully memory safe (other than don't go off the end of the vector which static rules can enforce by banning []). If I make a C wrapper I just lost all the memory safety and now I'm at higher risk. Plus the effort to build that wrapper is not zero (though there are some generators that help)

How about going off the end of the vector with an iterator, or modifying the vector while iterating it, or adding to the vector from two different threads or reading from one thread while another is modifying it or [...].

There is nothing memory safe whatsoever about std::vector<something> and std::string. Sure, they give you access to their allocated length, so they're better than something[] and char* (which often also know the size of their allocations, but refuse to tell you).

> going off the end of the vector with an iterator,

The point of an iterator is to make it hard to do that. You can, but it is easy to not do that.

> modifying the vector while iterating it

Annoying, but in practice I've not found it hard to avoid.

> adding to the vector from two different threads or reading from one thread while another is modifying it

Rust doesn't help here - they stop you from doing this, but if threads are your answer rust will just say no (or force you into unsafe). Threads are hard, generally it is best to avoid this in the first place, but in the places where you need to modify data from threads Rust won't help.

> rust will just say no

This is just not accurate, you can use atomic data types, Mutex<> or RwLock<> to ensure thread-safe access. (Or write your own concurrent data structures, and mark them safe for access from a different thread.) C++ has equivalent solutions but doesn't check that you're doing the right thing.

Only if using a hardened runtime with bounds checking enabled, without any calls to c_str().

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