Anything necessarily requiring lookup tables would be (comparably) slow. Unicode lookup tables are large, so it would be inherently slow for some inputs. For th

Anything necessarily requiring lookup tables would be (comparably) slow. Unicode lookup tables are large, so it would be inherently slow for some inputs. For the performance you should assume the input distribution (e.g. ASCII is frequent even in Unicode texts, so we detect a run of ASCII and go SIMD). You can also combine adjacent operations: instead of working with Unicode scalar values, you can directly accept UTF-8 string and optimize tables for them (Oniguruma regexp engine of Ruby fame does this).