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But you can index UTF-8 strings with precomputed bookmark indices (byte offsets) just fine. Point is, to precompute them, you would surely have iterated the str

But you can index UTF-8 strings with precomputed bookmark indices (byte offsets) just fine. Point is, to precompute them, you would surely have iterated the string before. What I mean is that "extract the 42th codepoint/glyph/whatever from this UTF-8 string" is a pointless operation for free-form strings because in a free-form string the character position is meaningless. (Basically all non-ASCII UTF-8 is pretty much a black box. You can't do serious computation with general Unicode because it's so complex and, as a consequence, ill-defined in practice).

slededit 8y ago
This is an advanced trick, but I've successfully done this as part of a binary search to find the glyph at the visual mid-point of the string. UTF-8 is self-synchronizing so you can detect if you cut a code point in half. You still need to handle things like ligatures which even UTF-32 won't speak to directly. Doesn't work well with BIDI languages, or Mongolian. Seriously if you haven't tested with Mongolian your code is probably wrong.