discrim

Construct enum variants from their discriminant

NOTE: I'm no longer maintaining this due to the existence of soccer; I've pretty much absorbed what I built here into that new crate, which I'll be maintaining from now on. If this crate looks interesting to you, you should go use soccer instead (it's better, I promise).

Overview

In order to initialize certain enum values from their discriminant, you basically have to manually write a giant match block that maps from each discriminant to the corresponding variant. This is both an annoyingly manual process and a potentially unsafe one; for example, what if you forget to update a discriminant value in the match after changing it in the enum definition?

This crate addresses that by providing a way to automatically generate that initialization code. More specifically, for fieldless, non-generic enums with a #[repr(...)] specified, it provides the FromDiscriminant trait and corresponding derive macro that automatically generates the initialization code as an implementation of the trait.

This project is licensed under the MIT License.

Example

A simple example, based on the use case that inspired this crate to begin with:

use discrim::FromDiscriminant;

#[derive(Debug, FromDiscriminant)]
#[repr(u8)]
enum Opcode {
    Add, Sub, Mul, Div,
}

fn main() {
    // prints "Ok(Mul)"
    println!("{:?}", Opcode::from_discriminant(2));

    // prints "Err(5)"
    println!("{:?}", Opcode::from_discriminant(5));
}