What is more important than "are bounds checks expensive or not" is that Rust gives you tools to do both, just like C++ gives you tools that do both. The defaul

What is more important than "are bounds checks expensive or not" is that Rust gives you tools to do both, just like C++ gives you tools that do both. The defaults are flipped, but both languages are equally capable. Dropbox famously found bounds checks to be expensive in one part of their Rust code, so they introduced the equivalent of a feature flag to toggle them.