It’s nice that rustc’s niche optimization lets smolstr be implemented with a simple enum, rather than having to do some unsafe union bit packing[0]. The only concession that had to be made to the compiler is using an enum for the InlineSize value to show that the last 3 bits of that aren’t used.

[0]: https://github.com/rust-analyzer/smol_str/blob/fde86a5c0cb8f...