如何在 Rust 中交换向量、切片或数组中的项目? [英] How can I swap items in a vector, slice, or array in Rust?

问题描述

我的代码如下所示:

fn swap<T>(mut collection: Vec<T>, a: usize, b: usize) {
    let temp = collection[a];
    collection[a] = collection[b];
    collection[b] = temp;
}

Rust 非常确定我不允许移出取消引用"或移出索引内容"，无论是什么.我如何让 Rust 相信这是可能的?

Rust is pretty sure I'm not allowed to "move out of dereference" or "move out of indexed content", whatever that is. How do I convince Rust that this is possible?

推荐答案

有一个 swap 为 &mut [T] 定义的方法.由于 Vec 可以可变解引用作为一个&mut [T]，可以直接调用这个方法:

There is a swap method defined for &mut [T]. Since a Vec<T> can be mutably dereferenced as a &mut [T], this method can be called directly:

fn main() {
    let mut numbers = vec![1, 2, 3];
    println!("before = {:?}", numbers);
    numbers.swap(0, 2);
    println!("after = {:?}", numbers);
}

要自己实现这一点，您必须编写一些不安全的代码.Vec::swap 是这样实现的:

To implement this yourself, you have to write some unsafe code. Vec::swap is implemented like this:

fn swap(&mut self, a: usize, b: usize) {
    unsafe {
        // Can't take two mutable loans from one vector, so instead just cast
        // them to their raw pointers to do the swap
        let pa: *mut T = &mut self[a];
        let pb: *mut T = &mut self[b];
        ptr::swap(pa, pb);
    }
}

它从向量中获取两个原始指针并使用 ptr::swap 以安全地交换它们.

It takes two raw pointers from the vector and uses ptr::swap to swap them safely.

还有一个 mem::swap(&mut T, &mut T) 当您需要交换两个不同的变量时.这不能在这里使用，因为 Rust 不允许从同一个向量中获取两个可变借用.

There is also a mem::swap(&mut T, &mut T) when you need to swap two distinct variables. That cannot be used here because Rust won't allow taking two mutable borrows from the same vector.

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