我有一个用Rust创建冒泡排序的编程任务。我在Rust方面没有太多的经验,所以这对我来说有点困难:
fn main() {
println!("Sort numbers ascending");
let num:[i32; 10] = [4, 65, 2, -31, 0, 99, 2, 83, 782, 1];
println!("Before: {:?}", num);
bubble_sort( num);
println!("After: {:?}\n", num);
}
fn swap( a: &mut i32, b: &mut i32){
let tmp: i32 = *b;
*b=*a;
*a=tmp;
}
fn bubble_sort(mut arr: [i32; 10]) {
for i in 0..arr.len() {
for j in 0..arr.len() - 1 - i {
if arr[j] > arr[j + 1] {
swap( &mut arr[j], &mut arr[j + 1]);
}
}
}
}
错误:
Compiling playground v0.0.1 (/playground)
error[E0499]: cannot borrow `arr[_]` as mutable more than once at a time
--> src/main.rs:19:24
|
19 | swap( &mut arr[j], &mut arr[j + 1]);
| ---- ----------- ^^^^^^^^^^^^^^^ second mutable borrow occurs here
| | |
| | first mutable borrow occurs here
| first borrow later used by call
|
= help: consider using `.split_at_mut(position)` or similar method to obtain two mutable non-overlapping sub-slices
For more information about this error, try `rustc --explain E0499`.
error: could not compile `playground` due to previous error
1条答案
按热度按时间i7uaboj41#
Rust借位检查器非常复杂,但它也有局限性。在这里,尽管对人类来说很明显没有可变别名,但借位检查器完全看不到这一事实。它看到
&mut arr[j]
和&mut arr[j + 1]
并得出结论:“您正尝试从arr
可变地借用两次”。错误消息确实指出了解决方案:
split_at_mut()
就是为这种情况而提供的。在幕后,它使用unsafe
以一种仍然合理并且不会导致UB的方式来弯曲上述规则。它接受一个索引来进行拆分,并返回2个不重叠的可变切片。这是来自文档的示例:因此,在您的情况下,不使用
&mut arr[j]
来获取对数字的可变引用,您可以执行以下操作:P.S.切片也有
.swap(i, j)
:-D