我如何“切换"通过枚举变体? [英] How do I "toggle" through enum variants?

问题描述

我想编写一个函数，将提供的值切换/切换到枚举中的下一个值，并在末尾回绕:

I'd like to write a function which toggles/switches the provided value to the next in the enum and wraps around at the end:

enum Direction { NORTH, SOUTH, EAST, WEST }

例如，NORTH => SOUTH, SOUTH => EAST, EAST => WEST, WEST => NORTH.

For example, NORTH => SOUTH, SOUTH => EAST, EAST => WEST, WEST => NORTH.

是否有比 在 Rust 中，有没有办法遍历枚举的值?

use Direction::*;
static DIRECTIONS: [Direction; 4] = [NORTH, SOUTH, EAST, WEST];

枚举不是应该被枚举"的吗?我依稀记得之前在 Rust 中看到过一个例子，但我似乎找不到它.由于 Rust 枚举更像是联合/变体，我想这会使事情复杂化.

Aren't enums suppose to be "enumerated"? I vaguely remember seeing an example before in Rust, but I can't seem to find it. Since Rust enums are more like unions/variants, I guess this complicates things.

推荐答案

我想这样的事情可以解决问题:

I guess something like this will do the trick:

#[macro_use]
extern crate num_derive;
extern crate num_traits;

use num_traits::FromPrimitive;

#[derive(Debug, Copy, Clone, FromPrimitive)]
enum Direction {
    NORTH = 0,
    SOUTH,
    EAST,
    WEST,
}

fn turn(d: Direction) -> Direction {
    FromPrimitive::from_u8((d as u8 + 1) % 4).unwrap()
}

fn main() {
    use Direction::*;
    for &d in [NORTH, SOUTH, EAST, WEST].iter() {
        println!("{:?} -> {:?}", d, turn(d));
    }
}

这不需要 unsafe，因为它使用自动派生的 FromPrimitive 特性.

This does not require unsafe as it uses the automatically derived FromPrimitive trait.

这篇关于我如何“切换"通过枚举变体?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！