Question

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并在结尾处回绕：

enum Direction { NORTH, SOUTH, EAST, WEST }

例如，NORTH =＆gt; SOUTH，SOUTH =＆gt; EAST，EAST =＆gt; WEST，WEST =＆gt; NORTH。

是否比In Rust, is there a way to iterate through the values of an enum?

中描述的手动创建静态数组更简单

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

Aren的枚举假设是＆＃34;枚举＆＃34;？我依稀记得在Rust之前看过一个例子，但我似乎无法找到它。由于Rust枚举更像是工会/变体，我想这会让事情复杂化。

Answer 1

我想这样的事情可以解决问题：

#[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特征。

Answer 2

弗拉基米尔的答案是正确的，但程序员必须记住在向enum添加新成员时更改幻数“4”。 turn的这个定义应该更容易维护：

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

fn turn(d: Direction) -> Direction {
    match FromPrimitive::from_u8(d as u8 + 1) {
        Some(d2) => d2,
        None => FromPrimitive::from_u8(0).unwrap(),
    }
}

Answer 3

我更愿意通过for i in attrs: match=re.search('(\d)GB',i) if match: if match.group(2)<8: print names语句显式编码下一个方向：

match

如何通过枚举变体“切换”？

3 个答案: