rust - "cannot move out of borrowed context"和 "use of moved value"

Question

我有以下代码:

pub enum Direction {
    Up, Right, Down, Left, None
}

struct Point {
    y: i32,
    x: i32
}

pub struct Chain {
    segments: Vec<Point>,
    direction: Direction
}

然后我实现了以下功能:

fn turn (&mut self, dir: Direction) -> i32 {
    use std::num::SignedInt;

    if dir == self.direction { return 0; }
    else if SignedInt::abs(dir as i32 - self.direction as i32) == 2 { return -1; }
    else {
        self.direction = dir;
        return 1;
    }
}

我得到错误:

error: cannot move out of borrowed content
foo.rs:45       else if SignedInt::abs(dir as i32 - self.direction as i32) == 2 { return 1; }
                                                        ^~~~
foo.rs:47:21: 47:24 error: use of moved value: `dir`
foo.rs:47           self.direction = dir;
                                         ^~~
foo.rs:45:26: 45:29 note: `dir` moved here because it has type `foo::Direction`, which is non-copyable
foo.rs:45       else if SignedInt::abs(dir as i32 - self.direction as i32) == 2 { return 1; }

我已经阅读了有关 Rust 所有权和借用的内容，但我仍然不太了解它们，因此我无法修复此代码。有人可以给我粘贴内容的工作变体吗？

Answer 1

如错误信息所述:

dir moved here because it has type foo::Direction, which is non-copyable

默认情况下没有类型是可复制的，作者必须选择标记特征 Copy。您几乎肯定希望 Direction 是可复制的，因此将 #[derive(Copy)] 添加到定义中。 Point 也可能是Copy。