Bitpacking the flag and data of an enum

language design
7

Optimizing layout of nested enums? and the related https://github.com/rust-lang/rfcs/issues/1230 share the same issues, although I don't see this particular suggestion. So far I can only think of "too weird to be really good ideas" suggestions for how to fix this issue. Better ergonomics around anonymous and/or _::Var enums might make this possible:

enum DayPadding {
    Space,
    None,
}

enum YearPadding {
    Space,
    None,
}

enum Specifier {
    Day { padding: DayPadding },
    Year { padding: YearPadding },
}

fn main() {
    dbg!(std::mem::size_of::<Specifier>());
}

Although that also prints

[src/main.rs:17] std::mem::size_of::<Specifier>() = 2

Which I guess is kind of a bug, but also a prerequisite for the OP to work ergonomic changes to help.