enum-from-discriminant-derive

Crate that provides a single Proc Macro to use on enums, TryFromDiscriminant.

It implements TryFrom<T> on an enum to turn numeric signed and unsigned values into an enum variant based on discriminant value.

Depending on the value of the biggest discriminant, TryFrom<u8>, TryFrom<u16>, TryFrom<u32>, TryFrom<u64>, TryFrom<usize>, TryFrom<i8>, TryFrom<i16>, TryFrom<i32>, TryFrom<i64> and TryFrom<isize> will be implemented.

Example:

use enum_from_discriminant_derive::TryFromDiscriminant;

#[derive(TryFromDiscriminant)]
enum MyCoolEnum {
    // Discriminant is implied to be 0 for FirstVariant...
    FirstVariant,
    // ... 1 for SecondVariant...
    SecondVariant,
    // ... and 16381 for ThirdVariant explicitly.
    ThirdVariant = 16381
}

// As the biggest discriminant (16381) does not fit in a u8, `TryFrom<u8>` and `TryFrom<i8>` will NOT be implemented.
// However, all others will be.

fn is_second(value: u16) -> bool {
    match MyCoolEnum::try_from(value).expect("not a valid discriminant") {
        MyCoolEnum::SecondVariant => true,
        _ => false,
    }
}