Comment by bluejekyll | Hacker News Reader

Comment by bluejekyll | Hacker News Reader

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> To me Rust is more a C++ replacement than a C replacement.

People make this comparison a lot, but it’s not fair. Rust is far simpler, in terms of number of features of the language, to that of C++. It’s fair to say that Rust is far more expressive than C, but this just represents an initial learning curve that is higher than C, but not as high as C++. The type system is fairly simple in Rust, but it can be used to create very complex things. It does take time to be able to read it, but the guarantees you get from it are very powerful.

> a C replacement should keep the procedural nature of C, with closures perhaps, but not go further in terms of paradigm

Why leave all of the language development of the last ~50 years on the table? Iterators in Rust are amazing, algebraic data types (enums) allow for simple state machine constructs, lifetimes guarantee memory safety, default immutable memory and single mutable owner mean no more concurrent memory modifications. It’s safer than Java, and as fast and memory constrained as C, what’s not to love?

These are amazing features, that allow for amazingly stable programs. To put it succinctly, you get to code once, and then rely on that code for a long time, to focus on building features, not bugs.

The only thing I ask of any C-replacement languages is that they make it possible to describe ABIs, message layouts, and on-disk formats in detail. C historically does that well enough, though not really all that well (e.g., bitfields and enums have issues, and struct packing is not always easy to get right). There is a lot of value to this!

The ability to mix object code from multiple languages (FFI) is critical, and that's why C is the common denominator for FFIs.

I won't do this justice, so I'll point you to the Rust book on this subject: https://doc.rust-lang.org/book/second-edition/ch19-01-unsafe...

In short, at the moment, if you want a stable ABI, you must export an un_mangled C interface. This is easy enough. One of my favorite sites is this for FFI stuff: http://jakegoulding.com/rust-ffi-omnibus/

It covers a bunch of languages, and suggests techniques for overcoming any complexity in exposing higher order types.

I wasn't criticizing Rust, and I'm aware of what you linked. The point I was making is that this sort of functionality is a sine qua non for C-replacement languages. That Rust has it is to its credit, and one reason that I think it is a very good C-replacement language.

C is the common denominator for FFI for OS that happen to be written in straight C, which then mix the C ABI with OS ABI.

That is not true in mainframes, Windows (ongoing replacement of Win32 with COM, it is lot of fun to do COM in C, more so UWP), Android (JNI, AIDL), Web (JavaScript/WebAssembly), iOS/macOS (Objective-C runtime), Fuchsia (IDL).

COM and WinRT are still based on the C ABI though. So anything that can do that, can do them - hopefully with more layers on top for convenience sake, of course...

Not quite, COM yes, although it is masochistic to do so without any higher level help.

UWP on the other hand extends COM to support inheritance and value types across calls, and the lowest Microsoft was willing to go on their high performance components was the Windows Runtime C++ Template Library, now replaced by C++/WinRT bindings and updated MIDL compiler.

The ABI is still C. Value types are just structs, and inheritance is implemented via aggregation - under the hood, it's all just interfaces and conventions on how they all play together. So any language that can do C FFI, can do WinRT. We did most of it with Python and ctypes as a prototype.

And you could even use that from C back in the day if you #included the "Windows.*.h" headers that shipped with the SDK - they had a bunch of #ifdef __cplusplus etc in them. Not sure if that stuff is still there or not.

Re: COM, that works because MSFT can a) commit to an ABI for C++, b) they can stick to a subset of C++ that makes that easy enough. Similarly for OS X.

The point isn't to stay in a C-like world. The point is that it must be possible to specify an ABI, file formats, and so on, in the host language. Yes, we can use external IDLs (even user them as DSLs if you like). I know all about and have worked with quite a lot of them (e.g., ASN.1, XDR, and many many others). But when you get down to a certain level, a light-weight approach really pays off. For example, at the system call level, and for many sufficiently simple file formats and such. At a higher end in complexity, on the other hand, then ASN.1 and friends pay off instead, mostly in a) obtaining interoperability with implementations written in other languages, b) managing extensibility.

Another thing is that some of us think about how things work at many levels. It's nice to be able to think about an interface and accurately picture what goes on at a low layer. It's difficult to do that with HLLs. But HLLs can easily have features that allow fine-grained control of or exposure of low level details, and that's what I'm saying I want to have as an option.

Why would you think that Rust is "far simpler" than C++? Exactly the same concepts (with extras on Rust's side because of the ML-like constructs) must be learned for both, except they're distributed differently on the learning curve.

And I wouldn't say that Rust's safer than Java either. Memory access errors are basically non-existant in Java and it has quite robust concurrency primitives and libraries.

That’s based on my experience of working with C++ on and off over the last 18 years and reattempting to learn some of the modern pieces of it, as compared to learning and working with Rust over the last 3.

I find Rust simpler, more concise, and nearly no footguns.

Edit, I didn’t see your Java comment:

> I wouldn't say that Rust's safer than Java either.

Here’s why it is safer: It has the same set of guarantees about memory safety as Java. In terms of concurrency, it is safer because of the single mutable reference guarantees across threads, enabled by a better type system. The type system is stronger, which allows for more details about code to be put into types, like algebraic data types of Rust, without the limitations of Java’s non-generic enums.

And the big one: no bare nulls allowed. This reduces a huge set of logic errors. Now Java is getting Value types in a future release which will allow for a true Option type in Java, ie one that cannot itself be null, the other points still stand.

On top of that, in large applications the GC can become an Achilles Heel, where it eventually pauses the application with dire consequences. Rust of course has no GC. And a great side effect of this is that Drop (java Finalizers) actually work in Rust, which is amazing.

Basically for these reasons, Rust is safer than Java.

Well, that's still personal opinion, even if grounded in experience.

My personal opinion is that they have similar complexity, but in general Rust decides to clearly define behaviour as much as possible and fail fast, preferably at compile time. This can be seen when comparing features: memory management is there (supported by the borrow checker), smart pointers are there, references & pointers are there, generics are there (even if not exactly the same), integer and floating point handling are there, concurrency is there (compile-time checking is nice), macros are there (albeit different and perhaps less error prone), string types are more complex than cpp, enums are more complex (but also more powerful), operator overloading is there, iterators are clearly more complex (and the functional aspects in general), etc.

So the average programmer will have to learn a similar amount of concepts or even more in Rust's case.

Where Rust is indeed simpler is error handling and building.

--- I figured you would bring up concurrency, and while Rust's compile-time verification is really nice, Java also has a simpler form in threading annotations. Additionally, I believe it's rare to use such low-level primitives in Java.

Nulls (and type system holes in general) are a correctness issue, not a safety issue, unless we want to argue that all bugs are safety issues.

GC pauses are a performance issue, as you already know.

Saying that Rust threading is safer than Java's is technically correct and Rust is probably a bit safer than Java because of that, but it's hard to argue that Rust should be chosen for a project because of that (this is the whole point of saying X is safer than Y). Java is super-simple to learn compared to Rust.

> that's still personal opinion, even if grounded in experience

I just wanted to make it clear how and why I've formed that opinion.

> unless we want to argue that all bugs are safety issues

Yes, I can definitely be accused of expanding the definition of safety to include all things that cause programs to crash in horrible ways. I look at it as differing levels of guarantees the language makes for you, and Rust makes many more at compile time than others. This adds to the learning curve you mention, is it worth it? Completely depends on if you see those guarantees as valuable.

> Why would you think that Rust is "far simpler" than C++?

C++ as a language is a lot more complicated. It has a lot of features with weird corner cases that interact in unfortunate ways.

> And I wouldn't say that Rust's safer than Java either.

Depends on what you mean with safe. If you mean memory safe, then they are about as safe. Rust has fewer runtime failures due to concurrency and null pointers though.

Not sure why the above comment is downvoted. The number of features in C++ isn't the root of the problem with C++. The real problem with C++ is that it both has a lot of features and that all of those features interact in subtle and surprising ways. Even if Rust had as many features as C++ (which it doesn't, not by a long shot; Rust is a medium-sized language like Python (though with a far less forgiving learning curve than Python)), one of the design philosophies of Rust is that features should interact in predictable ways, and if two features can't interact in predictable ways, then the compiler should do its damndest to prevent them from being used together and explain why.

The biggest issue is not how complicated it is, rather there is no good way to prevent people to write C in C++.

Rust also has features which interact in subtle and surprising ways. Generics and operator traits bumping into the "coherence" rules is my personal pet peave. I doubt any user would have predicted that interaction, and even though the compiler gives a detailed pointer to why, it's cold comfort.

Honestly, after hating C++ for years, trying to use Rust made me appreciate more about C++. I wish someone would make a language which took the best parts of both.

> even though the compiler gives a detailed pointer to why, it's cold comfort

We'll just have to agree to disagree, because having the compiler watch my back and preemptively guard against unforeseen pitfalls is about the warmest comfort I could ask for. :P

Generics and operator traits ought to be orthogonal and composable. Would you still be comforted if the compiler didn't let you mix for loops and arithmetic in one function? I mean, even if it gave you a detailed error message...

Ok then please prove that C++ is more complicated than Rust by listing which features of C++ are not available in Rust. It's nice that the compiler can tell me when I do something wrong, but I still have to know how to write it correctly in the first place. In Java it's more or less code and forget.

And yes, I meant memory safety.

The biggest ones people ask for are non-type templates, HKT, and sometimes move constructors.

Besides the (desirable) features already listed by someone else, here are a few others, some of which can have unfortunate interactions: implicit conversions, constructors, member initializer lists, inheritance, overloading, default arguments, capture lists, variadic templates.

You can still get NullPointerExceptions in Java, frequently.

Rust doesn't let you do that, at least not without conciously deciding to use unwrap() everywhere.

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