The other issue is that Rust pretty strongly expects slices to be laid out in memory as a flat array of some fixed-size element type. If something isn’t laid o

The other issue is that Rust pretty strongly expects slices to be laid out in memory as a flat array of some fixed-size element type. If something isn’t laid out that way, it can’t support all the operations a slice is supposed to support, ranging from the high-level operation of O(1) indexing, to the low-level operation of getting a raw pointer to the slice contents. In principle you could make &[ExtendedGraphemeCluster] special, but it would hamper the ability to write generic code that works on &[T] for any T. Besides, Rust likes to be explicit. Things that are different should look different. In addition, even if you gave up on O(1) indexing by grapheme cluster index, anything faster than O(n) indexing would require some sort of tree data structure to translate grapheme cluster indices to byte indices. Such a structure would be expensive to maintain and not needed the vast majority of the time; in a language that prioritizes performance, it simply couldn’t be part of the default string type no matter what the syntax.