Rust's "all strings must be valid UTF-8" rule allows them to remove a bounds check in their "get the Unicode code point corresponding to a byte index in the str

Rust's "all strings must be valid UTF-8" rule allows them to remove a bounds check in their "get the Unicode code point corresponding to a byte index in the string" function. Like, if you see a byte in the string that indicates it's the start of a 3-byte character, you don't have to worry about whether you'll have a buffer overrun when you try to read the following two bytes. As far as I know that's pretty much the only memory-safety-related benefit of that rule, and it's probably a wash since you still need to do that check at some other point in your program to safely construct a &str from non-constant string data. The impression I get from Rust people is that UTF-8 str is mostly about purity for purity's sake, and any performance improvement is at best a minor side benefit.