如何在 for 循环中进行可变借用？

Question

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; }
}

None 这些作品；我应该怎么做？

我收到如下错误：

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

Answer 1

您可能需要重新阅读 The Rust Programming Language，特别是以下部分：

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

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，可以调用iter_mut方法：

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

另请参阅：

请注意，您的变量不是向量。它是一个数组。

如何在 for 循环中进行可变借用？

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