# rotate-enum crate
A simple macro that implements `prev()` and `next()` methods to an enum in Rust
## Motivation
Sometimes you define an enum like this
```rust
enum Direction {
Up,
Left,
Down,
Right,
}
```
and you want to rotate them in some logic,
```rust
let up = Direction::Up;
let left = Direction::Left;
let down = Direction::Down;
let right = Direction::Right;
assert!(up.next() == left);
assert!(left.next() == down);
assert!(down.next() == right);
assert!(right.next() == up);
assert!(up.prev() == right);
assert!(left.prev() == up);
assert!(down.prev() == left);
assert!(right.prev() == down);
```
You can of course implement these methods manually, but it's repetitive and error prone.
Don't you think it should be automated?
This crate provides a `RotateEnum` derive macro to just do this.
## Shifting
This crate also provides `ShiftEnum`, which will exhaust at the end of the enum list,
rather than rotating.
```rust
let up = Direction::Up;
let left = Direction::Left;
let down = Direction::Down;
let right = Direction::Right;
assert!(up.next() == Some(left));
assert!(left.next() == Some(down));
assert!(down.next() == Some(right));
assert!(right.next() == None);
assert!(up.prev() == None);
assert!(left.prev() == Some(up));
assert!(down.prev() == Some(left));
assert!(right.prev() == Some(down));
```
## Usage
```rust
use rotate_enum::RotateEnum;
#[derive(RotateEnum)]
enum Direction {
Up,
Left,
Down,
Right,
}
```