Use enums for enumeration constants

[fiveop]

Just like we use bitflags! for flags, we could use enums for enumeration constants. They would provide a zero cost, type safe abstraction over the current primitive type constants.

A (partial) list of places to use enums:

• sys::mman::MADV_*
• sys::quota::Q_*
• sys::signal::SIG*

[kamalmarhubi]

👍

[kamalmarhubi]

Added a task list.

[kamalmarhubi]

Synonyms will not be allowed as variants. This results in E0081:

enum Foo {
    Bar = 0,
    Baz = 0,
    Quux = 1,
}

―playground

[kamalmarhubi]

We may be able to do something like this:

pub enum Foo {
    BAR = 0,
    QUUX = 1,
}
use Foo::*;

pub const BAZ: Foo = BAR;

fn main() {
    println!("{}", match BAR {
        // We can even *match* using the synonym!
        BAZ => "Is it a BAR? Could be a BAZ too!",
        _ => "Not Ba{r,z} =(",
    });
}

―playground