rust-borrow检查看起来非常聪明,它可以检查并平面读取和写入循环。但是我怎样才能绕过它呢?
以下代码运行良好:
fn main() {
let mut lines = [
vec![1, 2, 3],
vec![4, 5, 6],
vec![7, 8, 9],
];
for i in 0 .. lines.len() {
let line = &lines[i];
for item in line {
// if found odd number, push zero!
if item % 2 == 1 {
lines[i].push(0);
break; // works fine! if comment it, will error!
}
}
}
dbg!(lines);
}
当评论"中断"行时,将得到:
error[E0502]: cannot borrow `lines[_]` as mutable because it is also borrowed as immutable
--> src/main.rs:13:17
|
10 | let line = &lines[i];
| --------- immutable borrow occurs here
11 | for &item in line {
| ---- immutable borrow later used here
12 | if item == 5 {
13 | lines[1].push(55);
| ^^^^^^^^^^^^^^^^^ mutable borrow occurs here
error: aborting due to previous error
您不能绕过借用检查器。你要考虑它告诉你什么,并重新考虑你的程序以匹配。
这里它告诉你不能修改你当前正在迭代的东西(r ^w原则(,所以不要这么做。如果你想在每行中添加奇数的零,那么就这样做:计算行中的赔率,然后添加那么多零:
use std::iter::repeat;
fn main() {
let mut lines = [
vec![1, 2, 3],
vec![4, 5, 6],
vec![7, 8, 9],
];
for line in lines.iter_mut() {
let odds = line.iter().filter(|it| *it % 2 == 0).count();
line.extend(repeat(0).take(odds));
}
dbg!(lines);
}