错误类型不匹配：预期 'collections::vec::Vec<i32>'，发现 '&collections::vec::Vec<i32>'

Question

我正在尝试使用selection_sort 创建一个已排序的向量，同时保留原始未排序的向量：

fn main() {
    let vector_1: Vec<i32> = vec![15, 23, 4, 2, 78, 0];
    let sorted_vector = selection_sort(&vector_1);
    println!("{:?} is unsorted, \n{:?} is sorted.", &vector_1, &sorted_vector);
}

fn selection_sort(vector_1: &Vec<i32>) -> Vec<i32> {
    let mut vector = vector_1;
    let start = 0;
    while start != vector.len() {
        for index in (start .. vector.len()) {
            match vector[index] < vector[start] {
                true  => vector.swap(index, start),
                false => println!("false"), // do nothing
            }
        }
        start += 1;
    }
    vector
}

错误：

   Compiling selection_sort v0.1.0 (file:///home/ranj/Desktop/Rust/algorithms/sorting/selection_sort)
src/main.rs:21:5: 21:11 error: mismatched types:
 expected `collections::vec::Vec<i32>`,
    found `&collections::vec::Vec<i32>`
(expected struct `collections::vec::Vec`,
found &-ptr) [E0308]
src/main.rs:21     vector
                   ^~~~~~
src/main.rs:21:5: 21:11 help: run `rustc --explain E0308` to see a detailed explanation
error: aborting due to previous error
Could not compile `selection_sort`.

Answer 1

您的问题可以简化为（请在此处提问时查看并遵循如何创建MCVE）：

fn selection_sort(vector: &Vec<i32>) -> Vec<i32> {
    vector
}

您正在接受对类型的引用并尝试将其作为非引用返回。这只是一个直接的类型错误，与此相同：

fn something(value: &u8) -> u8 {
    value
}

T 和 &T 是不同的类型。

最终，您的代码现在没有意义。要将&Vec<T> 变成Vec<T>，您需要克隆它：

fn selection_sort(vector: &Vec<i32>) -> Vec<i32> {
    let mut vector = vector.clone();
    let mut start = 0;
    while start != vector.len() {
        for index in (start .. vector.len()) {
            match vector[index] < vector[start] {
                true  => vector.swap(index, start),
                false => println!("false"), // do nothing
            }
        }
        start += 1;
    }
    vector
}

但在 99.99% 的情况下，接受 &Vec<T> 是没有意义的；改为接受&[T]：

fn selection_sort(vector: &[i32]) -> Vec<i32> {
    let mut vector = vector.to_vec();
    // ...
}