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

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

And yes, I meant memory safety.

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