alt Hacker News> I don't know where it is that people have imagined this is something the C and C++ language designers went out of their way to foist upon you.
They did. Most other languages, the vast majority of which are also memory safe languages, go out of their way to do the opposite, and give meaning even to erroneous programs. Some things slip through the cracks, and generally language designers and implementers work hard to get rid of UB.
C/C++ is the only ecosystem that has fully embraced UB as a way of life. They are the only compilers that make full use of "UB is bad and cannot ever happen" as a core tenet in how optimizations are designed. Rust UB is at least a little different. Rust UB can only be the result of unsafe code and is meant to be limited in blast radius, and is absolutely not meant as a loophole for compilers to just do whatever to make the code faster.
C/C++ have a surprisingly large set of UB, too. Thankfully, the rest of the software world is rising up and the committees are starting to make things like gasp signed arithmetic overflow into defined behavior.
But don't hold your breath.
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C++26 and C++29 are in the process of turning a lot of that UB into erroneous behaviour, basically what safer languages have been doing for ages.
However, how many years it will take until those versions become widely deployed across major compilers, and used by developers?
> Rust UB […] is meant to be limited in blast radius, and is absolutely not meant as a loophole for compilers to just do whatever to make the code faster.
This isn't true. Rust UB is meant to only be possible to trigger via `unsafe` code, but if you do trigger it, the compiler is free to do whatever it wants, and in practice it will make full use of that freedom. Rustc uses LLVM, it shares most of its optimizations with Clang!
For, C we have already removed at lot of UB from the working draft for C2y. My hope is that only the UB is left that is difficult to remove without requiring extensive changes to code or compilers, and that this can then be addressed by a technical specification that defines a safe subset of C.
But note that UB also does not necessarily mean your program has no meaning. A good compiler can do something reasonable by defining the UB. There is no mandate in the specification that a compiler has to break things. It is also the user's responsibility to put pressure on compiler developers to do something reasonable.