C++ has editions too btw. C++11, C++14, C++17, etc. These are opt in and allowed to break compatibility, although that is very rarely done in practice.
That's one difference. And the other important differences are:
- Rust apps can depend on library "headers" written in other editions. That's the whole deal with editions! Breaking changes are local to your own code and don't fracture the ecosystem.
- Rust has a built-in tool that automatically migrates your code to the next edition while preserving its behavior. In C++, upgrading to the next standard is left as an exercise for the reader (just like everything else). And that's why it's done so rarely and so slowly.
Also it requires everything to be compiled with the same compiler, from source code.
There are tools available in some C++ compilers for migration like clang, note the difference between ISO languages with multiple implementations, and one driven by its reference compiler.
Not sure what you're talking about. Any specific examples?
> Also it requires everything to be compiled with the same compiler, from source code.
It's not related to editions at all. It's related to not having an implicit stable ABI.
It's possible have a dynamic Rust library that exposes a repr(C) interface, compile it into an .so using one version of the compiler, and then compile the dependent "pure Rust" crates using another compiler that's just going to read the metadata ("headers") of that library and link the final binary together. Same as in C and C++. You just can't compile any Rust code into a stable dynamic library, by defalut. (You can still always compile into a dylib that needs a specific compiler version)
You're correct that the possible changes in editions are very limited. But editions don't hinder interoperability in any way. They are designed not to. Today, there are no interoperability problems caused by editions specifically.
> compromises will be required, specially regarding possible incompatible semantic differences across editions.
That's just an assumption in your head. 4 editions later, it still hasn't manifested in any way.
ABIs and multiple versions of the language runtime, are part of what defines a language ecosystem, hence why editions don't really cover as much as people think they do.
We (as in the industry) will eventually get reliable ways to generate applications directly to machine code, just as optimizing compilers took a couple of decades to beat hand written Assembly, and generate reliable optimized code.
So editions, regardless of what they offer, might not be as relevant in such a timeframe from a couple of decades ahead.
What is the compiler supposed to generate if code from edition X calls code in edition X + 10, with a lambda written in X + 5, expecting using a specific language construct that has changed semantics across editions, maybe even more than once?
Everything compiling from source, same compiler.
You have gotten it across just fine.
We're trying to get across that no one is ever going to do "global" incompatible semantic changes in editions. That's been understood from the start. Exactly because of the problems that you describe.
Although, it's still possible to "sneak in" surprisingly useful semantic changes if they are local to the function body: https://doc.rust-lang.org/stable/edition-guide/rust-2024/tem...