I would add Ropes: https://github.com/rust-lang/rfcs/issues/653

Given the frequency of manipulating large bodies of text in contemporary programming I do not agree it is best left to a library implementation.

Without ropes as core std average rust developers will do what they did in java, c++, objC and simply use and abuse std::strings in all cases including those where it will perform poorly.

https://en.wikipedia.org/wiki/Rope_(data_structure)

[pdf] http://www.cs.rit.edu/usr/local/pub/jeh/courses/QUARTERS/FP/...