如何在 for 循环中进行可变借用? [英] How can I do a mutable borrow in a for loop?

问题描述

我试过了:

fn main() {
    let mut vec = [1, 2, 3];
    
    for mut x in &vec { *x = 3; }
    for mut &x in &vec { x = 3; }
    for mut *x in &vec { x = 3; }
    for mut x in mut &vec { *x = 3; }
    for mut x in &(mut vec) { *x = 3; }
}

这些都不起作用；我该怎么做?

None of these work; how should I do it?

我收到如下错误:

• mut 必须附加到每个单独的绑定
• 预期标识符，找到 *
• 预期表达式，找到关键字mut
• 不能分配给&引用后面的*x

• mut must be attached to each individual binding
• expected identifier, found *
• expected expression, found keyword mut
• cannot assign to *x which is behind a & reference

推荐答案

您可能需要重新阅读 Rust 编程语言，特别是以下部分:

You may want to re-read The Rust Programming Language, specifically the sections on:

• 可变性
• 可变引用
• 向量

我们还可以遍历可变向量中每个元素的可变引用，以便对所有元素进行更改.示例 8-9 中的 for 循环会将 50 添加到每个元素.

We can also iterate over mutable references to each element in a mutable vector in order to make changes to all the elements. The for loop in Listing 8-9 will add 50 to each element.

let mut v = vec![100, 32, 57];
for i in &mut v {
    *i += 50;
}

示例 8-9:迭代对向量中元素的可变引用

Listing 8-9: Iterating over mutable references to elements in a vector

要改变可变引用所引用的值，我们必须使用解引用运算符(*)来获取i中的值，然后才能使用+= 运算符.

To change the value that the mutable reference refers to, we have to use the dereference operator (*) to get to the value in i before we can use the += operator.

另外，你可以调用iter_mut 方法:

In addition, you can call the iter_mut method:

let mut v = vec![100, 32, 57];
for i in v.iter_mut() {
    *i += 50;
}

另见:

• 放置mut"和mut"有什么区别?在变量名之前和:"之后?
• iter 和 into_iter 有什么区别?

请注意，您的变量不是向量.它是一个数组.

Note that your variable is not a vector. It is an array.

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