I never heard of "German strings" in place of the small string optimization before! And there had been way too many proposals to add such types to the standard

I never heard of "German strings" in place of the small string optimization before! And there had been way too many proposals to add such types to the standard library [1] [2] [3] [4]. My understanding is that: 1. Both `Vec<u8>` and `String` should share the same layout as part of the standard library's contract. 2. Unlike `String`, the equivalent optimization for `Vec<T>` is more questionable especially when T might be any type. C++ standard libraries frequently do implement multiple layouts for std::string but not for std::vector<T> for the same reason. 3. Rust never allows an implicit copying of `String` in the first place, which greatly benefits from the SSO, so the lack of SSO in Rust is less important compared to C++. [1] https://github.com/rust-lang/rust/issues/4991 https://github.com/rust-lang/rust/issues/4991 [2] https://github.com/rust-lang/rust/issues/20198 https://github.com/rust-lang/rust/issues/20198 [3] https://github.com/rust-lang/rfcs/pull/2990 https://github.com/rust-lang/rfcs/pull/2990 [4] https://github.com/rust-lang/unsafe-code-guidelines/issues/499 https://github.com/rust-lang/unsafe-code-guidelines/issues/4...