Validating should be pretty trivial. Explicitly handling all cases would look something like this: #[inline] const fn is_valid_scalar(c: u32) -> bool {

Validating should be pretty trivial. Explicitly handling all cases would look something like this: #[inline] const fn is_valid_scalar(c: u32) -> bool { match c { 0..=0xD7FF => true, 0xD800..=0xDFFF => false, // surrogate pairs 0xE000..=0x10FFFF => true, 0x110000..=u32::MAX => false, // outside of Unicode range } } But this could be reduced down to a simple if statement that tests for the invalid ranges.