num_enum

Procedural macros to make inter-operation between primitives and enums easier.

Turning an enum into a primitive

```rust extern crate numenum; use numenum::IntoPrimitive;

[derive(IntoPrimitive)]

[repr(u8)]

enum Number { Zero, One, }

[test]

fn convert() { let zero: u8 = Number::Zero.into(); assert_eq!(zero, 0u8); } ```

num_enum's IntoPrimitive is more type-safe than using as, because as will silently truncate - num_enum only derives From for exactly the discriminant type of the enum.

Turning a primitive into an enum with try_from (nightly only)

```rust

![feature(try_from)]

extern crate num_enum;

use num_enum::TryFromPrimitive; use std::convert::TryInto;

[derive(Debug, Eq, PartialEq, TryFromPrimitive)]

[repr(u8)]

enum Number { Zero, One, }

[test]

fn convert() { let zero: Number = 0u8.tryinto().unwrap(); asserteq!(zero, Ok(Number::Zero));

let three: Result<Number, String> = 3u8.try_into();
assert_eq!(three, Err("No value in enum Number for value 3".to_owned()));

} ```

Turning a primitive into an enum (stable rust)

Unfortunately, try_from is not yet stable (see https://github.com/rust-lang/rust/issues/33417), so num_enum can also derive a custom trait which can be used in stable rust. It's a little ugly, but it does the job! It adds a function called try_into_{enum_name} which you can use. If you're converting outside of the module where the enum was defined, you may also need to use your_module::TryInto{enum_name};.

```rust extern crate num_enum;

use num_enum::CustomTryInto;

[derive(Debug, Eq, PartialEq, CustomTryInto)]

[repr(u8)]

enum Number { Zero, One, }

[test]

fn convert() { let zero: Result = 0u8.tryintoNumber(); assert_eq!(zero, Ok(Number::Zero));

let three: Result<Number, String> = 3u8.try_into_Number();
assert_eq!(three, Err("No value in enum Number for value 3".to_owned()));

} ```

Optional features

Some enum values may be composed of complex expressions, for example:

rust enum Number { Zero: (0, 1).0, One: (0, 1),1, }

To cut down on compile time, these are not supported by default, but if you enable the complex-expressions feature of your dependency on num_enum, these should start working.