The topic of the Rust experiment was just discussed at the annual Maintainers Summit. The consensus among the assembled developers is that Rust in the kernel is no longer experimental — it is now a core part of the kernel and is here to stay. So the “experimental” tag will be coming off. Congratulations are in order for all of the Rust for Linux team.
IIRC you can speed up such checks by putting an assertion in front that checks for the largest index - this will make repeated checks for smaller indices unnecessary. Also, bound checks are often not even visible on modern CPUs because speculative execution, branch prediction, and out-of-order execution. The CPU just assumes that the checks will succeed, and works on the next step.
I had no idea about the assertion! Thanks.
Yes, this is plain wrong or often unimportant on modern architecture, you’re right. I, certainly mistakenly, thought this was one of the reasons for the idiomatic version involving function composition, which is the thing I, subjectively, don’t enjoy as much.
I stand corrected.
The function composition style comes from functional programming and Rust’s OCaml heritage. It can make it easier to reason about invriants and possible sets of values of the result of a computation step.
Rust transforms these to the same or a close equivalent of hand-written loops.
Similar methods are used in specialized, high-performance C++ libraries such as blitz++ and Eigen. But if you mess up bounds, you will get UB with them.