Macro usize_try_from

macro_rules! usize_try_from {
    ($(#[$meta:meta])* $vis:vis enum $name:ident {
    $($(#[$vmeta:meta])* $vname:ident $(= $val:expr)?,)*
    }) => { ... };
}

Associates usize values to each enum value and declares a TryFrom<usize> implementation for this enum allowing a try_from(usize) to enum conversion.

Example:

use workflow_core::enums::usize_try_from;

usize_try_from!{
    #[derive(Debug, Clone, PartialEq)]
    enum MyEnum {
        A,  // 0usize
        B,  // 1usize
        C,  // 2usize
    }
}

let v1 = MyEnum::B;
let n: usize = v1.clone() as usize;
let v2 = MyEnum::try_from(n).unwrap();
assert_eq!(v1, v2);