How do you define operator[] for a string that's in a variable-width encoding such as UTF-8? One of the basic assumptions in std::string that I intend to honor is that operator[] returns a reference to the actual data, not a copy. For fixed-width encodings such as ASCII, UCS2, or UCS4, this is not a problem; I simply return a unsigned char/short/long. However, for variable-width encodings, I need to return a range of bytes, and presumably a size as well. I could do this with covariant return...