Enums

An enum becomes a Rust enum with one variant per enumerator and explicit discriminants, followed by the impls that give it C semantics. Given

enum Color { RED, GREEN, BLUE };

both models produce

#![allow(unused)]
fn main() {
#[derive(Clone, Copy, PartialEq, Debug, Default)]
enum Color {
    #[default]
    RED = 0,
    GREEN = 1,
    BLUE = 2,
}
impl From<i32> for Color {
    fn from(n: i32) -> Color {
        match n {
            0 => Color::RED,
            1 => Color::GREEN,
            2 => Color::BLUE,
            _ => panic!("invalid Color value: {}", n),
        }
    }
}
libcc2rs::impl_enum_inc_dec!(Color);
}

and the refcount model adds an impl ByteRepr for Color that converts through the i32 value.

The first enumerator is the #[default], which is what a zero-initialized or default-constructed enum variable holds. From<i32> is the integer-to-enum cast; a value that matches no enumerator panics, where C would silently keep the integer. impl_enum_inc_dec! implements the four ++/-- forms by stepping through the enumerators. Enum-to-integer casts need no impl and become as i32.

enum class is translated the same way; enumerators are always spelled Color::RED on the Rust side, scoped or not. In C, an anonymous enum named only through a typedef (typedef enum { ... } Tag;) is emitted as Tag_enum, and an anonymous enum with no name at all as anon_N (see Naming).