This crate exports a macro enum_from_primitive! that wraps an enum declaration and automatically adds an implementation of num::FromPrimitive (reexported here), to allow conversion from primitive integers to the enum. It therefore provides an alternative to the built-in #[derive(FromPrimitive)], which requires the unstable std::num::FromPrimitive and is disabled in Rust 1.0.

https://andersk.github.io/enum_primitive-rs/enum_primitive/

Add the following to your Cargo.toml file:

[dependencies]
enum_primitive = "*"

Import the crate using #[macro_use] extern crate enum_primitive, and wrap your enum declaration inside the enum_from_primitive! macro.

#[macro_use] extern crate enum_primitive;
extern crate num;
use num::FromPrimitive;

enum_from_primitive! {
#[derive(Debug, PartialEq)]
enum FooBar {
    Foo = 17,
    Bar = 42,
    Baz,
}
}

fn main() {
    assert_eq!(FooBar::from_i32(17), Some(FooBar::Foo));
    assert_eq!(FooBar::from_i32(42), Some(FooBar::Bar));
    assert_eq!(FooBar::from_i32(43), Some(FooBar::Baz));
    assert_eq!(FooBar::from_i32(91), None);
}