String class based on graphemes?

Question

I'm wondering why we don't have some string classes that represent a string of Unicode grapheme clusters instead of code points or characters. It seems to me that in most applications it would be easier for programmers to access components of a grapheme when necessary than to have to organize them from code points, which appears necessary even if only to avoid casually breaking a string in "mid-grapheme" (at least in theory). Internally a string class might use a variable length encoding such as UTF-8, UTF-16, or in this context even UTF-32 is variable length; or implement subclasses for all of them (and optionally configure the choice at run-time so that different languages could use their optimal encodings). But if programmers could "see" grapheme units when inspecting a string, wouldn't string handling code in general be closer to achieving correctness, and without much extra complexity?

References:
Characters and Combining Marks
Unicode implementer's guide part 4: grapheme breaking
UnicodeString Class Reference
Enumerating a string by grapheme instead of character
Strings and character encoding in C++

Answer 1

I don't think so, because grapheme breaks are not the only measure of correctness. And, there are different user perceived characters depending on the language/script being used. If you are concerned about normalization mode you will also want to see Normalizer::concatenate. So I would recommend just working in code units most of the time and calculating breaks when need be.