UnscopedEnum

unscoped_enum.rs

//--------------------------------------------------------
#[derive(Debug, PartialEq, Eq, Copy, Clone)]
#[repr(u8)]
enum UnscopedEnum {
    AAA = 1,
    BBB = 2,
    CCC = 3,
}

const AAA: UnscopedEnum = UnscopedEnum::AAA;
const BBB: UnscopedEnum = UnscopedEnum::BBB;
const CCC: UnscopedEnum = UnscopedEnum::CCC;

impl From<u8> for UnscopedEnum {
    fn from(v: u8) -> UnscopedEnum {
        // DANGER!!
        unsafe { std::mem::transmute(v) }
    }
}

impl std::fmt::Display for UnscopedEnum {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match *self {
            AAA => f.write_str(stringify!(AAA)),
            BBB => f.write_str(stringify!(BBB)),
            CCC => f.write_str(stringify!(CCC)),
        }
    }
}
//--------------------------------------------------------

fn main() {
    let e: UnscopedEnum = 1.into();
    println!("e={}", e);
    if e != BBB {
        println!("e not equal {}", BBB);
    } else {
        println!("e equal {}", BBB);
    }
}