错误：不匹配的类型：在尝试实现冒泡排序时发现“&usize”预期的“usize”

Question

我正在尝试在 Rust 中实现冒泡排序算法，但我遇到了类型不匹配错误。有人可以帮助实施吗？

此外，它的实现方式与我在 Python 中实现的方式相同。我确信有一种简单的方式来实现这一点。

fn main() {
    let mut list = [15, 3, 2, 1, 6, 0];
    bubble_sort(list);
    println!("order list is: {:?}", &list);
}

fn bubble_sort(list: &mut [usize]) {
    for i in 0..&list.len() {
        for j in 0..(&list.len()-1) {
            if &list[&j] > &list[&j+1] {
                &list.swap( &list[&j], &list[&j+1] );
            }
        }
    }
}

编译器错误：

Compiling bubble_sort v0.1.0 (file:///home/ranj/Desktop/Rust/algorithms/sorting/bubble_sort)
src/main.rs:5:17: 5:21 error: mismatched types:
 expected `&mut [usize]`,
    found `[_; 6]`
(expected &-ptr,
    found array of 6 elements) [E0308]
src/main.rs:5     bubble_sort(list);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~

src/main.rs:5:17: 5:21 help: run `rustc --explain E0308` to see a detailed explanation
src/main.rs:11:14: 11:30 error: start and end of range have incompatible types: expected `_`, found `&usize` (expected integral variable, found &-ptr) [E0308]
src/main.rs:11     for i in 0..&list.len() {
~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~

note: in expansion of for loop expansion
src/main.rs:11:5: 17:6 note: expansion site
src/main.rs:11:14: 11:30 help: run `rustc --explain E0308` to see a detailed explanation
src/main.rs:13:17: 13:25 error: the trait `core::ops::Index<&usize>` is not implemented for the type `[usize]` [E0277]
src/main.rs:13             if &list[&j] > &list[&j+1] {
~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~

note: in expansion of for loop expansion
src/main.rs:12:9: 16:10 note: expansion site
note: in expansion of for loop expansion
src/main.rs:11:5: 17:6 note: expansion site
src/main.rs:13:17: 13:25 note: the type `[usize]` cannot be indexed by `&usize`
src/main.rs:13             if &list[&j] > &list[&j+1] {
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~

note: in expansion of for loop expansion
src/main.rs:12:9: 16:10 note: expansion site
note: in expansion of for loop expansion
src/main.rs:11:5: 17:6 note: expansion site
src/main.rs:13:17: 13:25 error: the trait `core::ops::Index<&usize>` is not implemented for the type `[usize]` [E0277]
src/main.rs:13             if &list[&j] > &list[&j+1] {
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~

note: in expansion of for loop expansion
src/main.rs:12:9: 16:10 note: expansion site
note: in expansion of for loop expansion
src/main.rs:11:5: 17:6 note: expansion site
src/main.rs:13:17: 13:25 note: the type `[usize]` cannot be indexed by `&usize`
src/main.rs:13             if &list[&j] > &list[&j+1] {
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~

note: in expansion of for loop expansion
src/main.rs:12:9: 16:10 note: expansion site
note: in expansion of for loop expansion
src/main.rs:11:5: 17:6 note: expansion site
src/main.rs:14:30: 14:38 error: the trait `core::ops::Index<&usize>` is not implemented for the type `[usize]` [E0277]
src/main.rs:14                 &list.swap( &list[&j], &list[&j+1] );
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~

note: in expansion of for loop expansion
src/main.rs:12:9: 16:10 note: expansion site
note: in expansion of for loop expansion
src/main.rs:11:5: 17:6 note: expansion site
src/main.rs:14:30: 14:38 note: the type `[usize]` cannot be indexed by `&usize`
src/main.rs:14                 &list.swap( &list[&j], &list[&j+1] );
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~

note: in expansion of for loop expansion
src/main.rs:12:9: 16:10 note: expansion site
note: in expansion of for loop expansion
src/main.rs:11:5: 17:6 note: expansion site
src/main.rs:14:30: 14:38 error: the trait `core::ops::Index<&usize>` is not implemented for the type `[usize]` [E0277]
src/main.rs:14                 &list.swap( &list[&j], &list[&j+1] );
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~

note: in expansion of for loop expansion
src/main.rs:12:9: 16:10 note: expansion site
note: in expansion of for loop expansion
src/main.rs:11:5: 17:6 note: expansion site
src/main.rs:14:30: 14:38 note: the type `[usize]` cannot be indexed by `&usize`
src/main.rs:14                 &list.swap( &list[&j], &list[&j+1] );
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~

note: in expansion of for loop expansion
src/main.rs:12:9: 16:10 note: expansion site
note: in expansion of for loop expansion
src/main.rs:11:5: 17:6 note: expansion site
src/main.rs:14:40: 14:51 error: mismatched types:
 expected `usize`,
    found `&usize`
(expected usize,
    found &-ptr) [E0308]
src/main.rs:14                 &list.swap( &list[&j], &list[&j+1] );
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~

note: in expansion of for loop expansion
src/main.rs:12:9: 16:10 note: expansion site
note: in expansion of for loop expansion
src/main.rs:11:5: 17:6 note: expansion site
src/main.rs:14:40: 14:51 help: run `rustc --explain E0308` to see a detailed explanation
error: aborting due to 7 previous errors
Could not compile `bubble_sort`.

Answer 1

除了 Lukas 提到的之外，还有一些其他问题：

---

冒泡排序函数的参数类型必须为&mut [usize]。 list 有 [usize] 类型，所以你必须转换它：当你调用冒泡排序函数时。

bubble_sort(&mut list);

---

当您在列表中调用swap 时，您应该传入要交换的事物的索引，而不是值本身。

list.swap( j, j+1 );

Answer 2

在不知道编译器错误的确切原因的情况下：您应该删除很多&——例如在索引括号[ ]中。

编译器只是说它需要一个usize 类型的变量，但找到了&usize 类型之一，它是对该类型的引用。索引运算符（[ ] 括号）采用usize 类型的参数。但是您可以通过添加& 来提供参考。

Answer 3

谢谢大家，下面是正确的实现：

fn main() {
    let mut list = [15, 3, 2, 1, 6, 0];
    bubble_sort(&mut list);
    println!("Sorted list is: {:?}", &list);
}

fn bubble_sort(list: &mut [usize]) {
    for _ in 0..list.len() {
        for j in 0..(&list.len()-1) {
            if list[j] > list[j+1] {
                list.swap( j, j+1 );
            }
        }
    }
}