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I think a number of companies have proven that it isn't a "big problem" by successfully interoping Rust and C++. What you describe might be an inconvenience, bu

I think a number of companies have proven that it isn't a "big problem" by successfully interoping Rust and C++. What you describe might be an inconvenience, but this goes back to what I was saying about how Google could achieve their outcome with less effort by customizing their own version of bindgen. Google could give up some safety in exchange for the desired, incremental outcomes. If they needed to fork the Rust compiler to pessimize a few optimizations that the Rust compiler would normally do (that would invalidate such unsafe C++ code with additional UB), even that would be far less effort than inventing their own entire new language and ecosystem from scratch. That is without considering how Google could work with the Rust Core Team to contribute solutions for ergonomic issues they're encountering in the interop process. When the alternative is "building an entire, general purpose programming language", there are a lot of other things you can do that would be much easier. And, as previously mentioned, Carbon is only addressing the low hanging fruit... it isn't stated anywhere I've seen that they even intend to achieve parity with Rust. All of this effort, just for a lesser outcome. I'm sorry that I'm frustrated at big companies choosing to take half measures that seem even more expensive than the full measure. I have used Rust professionally for years; I'm clearly biased, but it's not that hard. The level of safety that Rust provides should be table stakes in discussions of unmanaged languages... not the ceiling for what we can possibly imagine, but Carbon is a statement that Rust's bar is too high for Google to reach, and that's pretty depressing.

zozbot234 4y ago
I'm not talking about giving up safety, I'm talking about library API's that are simply not usable by code that involves, e.g. possibly aliased pointers, or pinned data, other than by invoking possible UB, merely because those things are "unidiomatic" in Rust (even though, if the unsafety is properly contained, it's quite possible to e.g. write proofs of correctness for such code, or verify it via a model checker). It's a recurring topic on the Rust Internals forum. "Pessimizing" the compiler is not a solution, UB is still UB. You'd have to actually look at what the code does in detail and provide a generalized interface to it, possibly needing to introduce new "unsafe" blocks in the process and prove their safety.
- coder543 4y ago
  > other than by invoking possible UB I addressed this when I talked about a compiler fork. Google could maintain a patchset against the Rust compiler that makes this behavior well-defined in a way that suits them during the transition period as C++ code is rewritten. Or they could work with the Rust Core Team to address this issue in a way that is favorable to them over the next year or two. Either of these options are much less work than developing an entirely new language and ecosystem. As far as I can tell, Google tried neither option. Still, Mozilla and others have gotten along just fine as it is.
  - joshuamorton 4y ago
    > Rust compiler that makes this behavior well-defined in a way that suits them during the transition period as C++ code is rewritten To be clear, this is "forever". I don't think anyone involved has an expectation to truly get rid of Google's existing C++ codebase ever. So the question is, do you really want Google to fork rustc to implement some google specific UB handling? Is that good or fair to the rust community? Even if it was, the HN comments would be along the line of "Google is using an embrace/extend/extinguish approach to force rust to do certain things bypassing the normal rust language processes", and they'd in some ways be correct! Could rust really choose different semantics from the already existing one, or would google-rust implicitly be a standard that rust would need to support? Would that be a good idea for anyone? > Still, Mozilla and others have gotten along just fine as it is. IIUC, one of the driving factors behind this is that vanilla C++ is too slow, and ABI compatibility prevents up-streaming certain performance improvements. So what works for Mozilla probably doesn't work here, because what works for Mozilla has a performance penalty. Sure it's small, but that's going in the wrong direction.
    - coder543 4y ago
      > To be clear, this is "forever" I guess I didn't finish my thought in that comment, because it isn't forever... it's only until either the C++ is gone, or the Rust language has developed an equally acceptable alternative (which could be upstreamed by Google, or come from somewhere else). And realistically, the C++ would never have to go away entirely for this UB handling fork to become unnecessary, depending on the driving factors. Some code paths are more performance sensitive than others, and these tend to represent a small portion of the overall code. Once the performance sensitive code paths are rewritten, it matters less whether there is a small performance penalty for the remaining C++ code that is less sensitive to performance. But, at Google Scale, the cost of the developer-hours to maintain that fork would probably be less than the cost of the small increase in CPU hours that removing the fork would result in, so... yeah, maybe forever or until there is an upstream solution. Maintaining a patchset like this would still cost way less than maintaining an entire compiler and all the language tooling needed to support that language... does anyone really disagree? A new language is far more than just a compiler, let alone a patch for a compiler. > Would that be a good idea for anyone? IMHO, it definitely seems better than Carbon.

zozbot234 4y ago

I'm not talking about giving up safety, I'm talking about library API's that are simply not usable by code that involves, e.g. possibly aliased pointers, or pinned data, other than by invoking possible UB, merely because those things are "unidiomatic" in Rust (even though, if the unsafety is properly contained, it's quite possible to e.g. write proofs of correctness for such code, or verify it via a model checker). It's a recurring topic on the Rust Internals forum. "Pessimizing" the compiler is not a solution, UB is still UB. You'd have to actually look at what the code does in detail and provide a generalized interface to it, possibly needing to introduce new "unsafe" blocks in the process and prove their safety.

coder543 4y ago
> other than by invoking possible UB I addressed this when I talked about a compiler fork. Google could maintain a patchset against the Rust compiler that makes this behavior well-defined in a way that suits them during the transition period as C++ code is rewritten. Or they could work with the Rust Core Team to address this issue in a way that is favorable to them over the next year or two. Either of these options are much less work than developing an entirely new language and ecosystem. As far as I can tell, Google tried neither option. Still, Mozilla and others have gotten along just fine as it is.
- joshuamorton 4y ago
  > Rust compiler that makes this behavior well-defined in a way that suits them during the transition period as C++ code is rewritten To be clear, this is "forever". I don't think anyone involved has an expectation to truly get rid of Google's existing C++ codebase ever. So the question is, do you really want Google to fork rustc to implement some google specific UB handling? Is that good or fair to the rust community? Even if it was, the HN comments would be along the line of "Google is using an embrace/extend/extinguish approach to force rust to do certain things bypassing the normal rust language processes", and they'd in some ways be correct! Could rust really choose different semantics from the already existing one, or would google-rust implicitly be a standard that rust would need to support? Would that be a good idea for anyone? > Still, Mozilla and others have gotten along just fine as it is. IIUC, one of the driving factors behind this is that vanilla C++ is too slow, and ABI compatibility prevents up-streaming certain performance improvements. So what works for Mozilla probably doesn't work here, because what works for Mozilla has a performance penalty. Sure it's small, but that's going in the wrong direction.
  - coder543 4y ago
    > To be clear, this is "forever" I guess I didn't finish my thought in that comment, because it isn't forever... it's only until either the C++ is gone, or the Rust language has developed an equally acceptable alternative (which could be upstreamed by Google, or come from somewhere else). And realistically, the C++ would never have to go away entirely for this UB handling fork to become unnecessary, depending on the driving factors. Some code paths are more performance sensitive than others, and these tend to represent a small portion of the overall code. Once the performance sensitive code paths are rewritten, it matters less whether there is a small performance penalty for the remaining C++ code that is less sensitive to performance. But, at Google Scale, the cost of the developer-hours to maintain that fork would probably be less than the cost of the small increase in CPU hours that removing the fork would result in, so... yeah, maybe forever or until there is an upstream solution. Maintaining a patchset like this would still cost way less than maintaining an entire compiler and all the language tooling needed to support that language... does anyone really disagree? A new language is far more than just a compiler, let alone a patch for a compiler. > Would that be a good idea for anyone? IMHO, it definitely seems better than Carbon.