crubit

nate. In all other cases (that I can think of), Rust prevents undefined behavior at runtime not by changing it to do something defined at runtime instead, but by requiring the programmer to prove to the compiler that the undefined behavior can't happen. This may be annoying, and may encourage programmers to resort to things like RefCell that have runtime costs in order to avoid the difficulty of such proofs, but it should never stop you from doing the unsafe maximum-performance thing if you really want to. Rust can also do some optimizations that C++ can't; it has additional forms of undefined behavior, like mutable aliasing and invalid UTF-8 strings, that the compiler can in principle exploit. Probably the more important advantage, though, is that Rust's maintainers can freely make changes to its compiler and standard library that don't preserve compatibility with existing compiled code (as opposed to existing source code), because the language has never promised ABI stability and (unlike C++) doesn't have an entrenched community of users who count on ABI stability and will complain if it's broken. Almost all Rust binaries statically link all dependencies except for libc, and build all statically-linked dependencies other than the standard library (which is tightly coupled to the compiler) from source on every compilation, and this has been the case since the language's beginning. For an explanation of why C++'s need to preserve backwards compatibility for compiled code inhibits optimization, see: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p20... As for your other point, I think Rust will need smoother C++ interop than it currently has before it can displace C++, but there's hope. Here's the project I'm currently most optimistic about: https://github.com/google/crubit

with C++ (http://cxx.rs) and ongoing research into automating this interoperability (https://github.com/google/autocxx, https://github.com/google/crubit). Feels like there's enough effort in all areas. I don't understand a request that says "drop everything else, focus on what I think is important". That's not how open source efforts work. People work on what they think is most impactful, what they enjoy working on. As long as they're not hurting any other use case, why stop them?