SSO means that pretty every string operation has multiple code paths, which can be highly unpredictable. Basically it is a trade-off between memory usage and pe

SSO means that pretty every string operation has multiple code paths, which can be highly unpredictable. Basically it is a trade-off between memory usage and performance, and the standard library is not really a good place to make that trade-off. By comparison many C++ codes (still) copy strings all over the place for no good reason, so SSO in the standard library has a much greater appeal.