If you want it safe, then the C++ version should also add a (single) length check. To fix rust's multiple points of failure, move the check to the top, by add s

If you want it safe, then the C++ version should also add a (single) length check. To fix rust's multiple points of failure, move the check to the top, by add something like 'let length_check = slice[5]', moving the 'slice[5]=5' to the top (or something nicer, don't know rust), and you will get only a single point of failure and a single check, same as safe C++ with matching API. If you want to have 0 runtime checks, like the C++ example, you can 1) make it unsafe and actively dangerous, like the C++ version 2) change the API so minimum length is guaranteed (probably possible in rust, harder in C++) 3) have the function private/inline where sufficient length is known/can be deduced and the check will be omitted