rust - move 发生是因为 value 的类型为 Vec，它没有实现 `Copy` 特征

Question

我正在编写一个非常简单的递归程序来查找两个数字之间的所有素数：

use std::cmp::PartialOrd;
use std::ops::{Add, Div, Rem, Sub};

fn _is_prime<T>(n: T, dividend: T, one: T) -> bool
where
    T: Copy + Rem<Output = T> + Sub<Output = T> + PartialOrd,
{
    if dividend == one {
        true
    } else {
        if n % dividend < one {
            false
        } else {
            _is_prime(n, dividend - one, one)
        }
    }
}

fn _primes_between<'a, T>(a: T, b: T, one: T, v: &'a mut Vec<T>) -> &'a mut Vec<T>
where
    T: Copy + Rem<Output = T> + Add<Output = T> + Sub<Output = T> + PartialOrd,
{
    if a <= b {
        if _is_prime(a, a - one, one) {
            v.push(a);
        }

        _primes_between(a + one, b, one, v)
    } else {
        v
    }
}

fn primes_between<T>(a: T, b: T) -> Vec<T>
where
    T: Copy + Div<Output = T> + Rem<Output = T> + Add<Output = T> + Sub<Output = T> + PartialOrd,
{
    let one = a / a;

    let mut v: Vec<T> = Vec::new();

    *_primes_between(a, b, one, &mut v)
}

fn main() {
    primes_between(3, 13).iter().for_each(|i| println!("{}", i));
}

问题是：

error[E0507]: cannot move out of a mutable reference
  --> src/main.rs:42:5
   |
42 |     *_primes_between(a, b, one, &mut v)
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ move occurs because value has type `std::vec::Vec<T>`, which does not implement the `Copy` trait

我该如何解决这个错误？

标签： rust

Answer 1

我不是 100% 确定，但我认为问题在于_primes_between()返回第 31 行代码试图复制的引用。（通过*操作员获得所有权）您可以通过调用.clone()结果来解决问题，但我认为在这种情况下您不需要_primes_between()返回值 - 您只需将适当的条目添加到v参数中即可。就像是

fn _primes_between<T>(a: T, b: T, one: T, v: &mut Vec<T>)
where
    T: Copy + Rem<Output = T> + Add<Output = T> + Sub<Output = T> + PartialOrd,
{
    if a <= b {
        if _is_prime(a, a - one, one) {
            v.push(a);
        }

        _primes_between(a + one, b, one, v);
    }
}

fn primes_between<T>(a: T, b: T) -> Vec<T>
where
    T: Copy + Div<Output = T> + Rem<Output = T> + Add<Output = T> + Sub<Output = T> + PartialOrd,
{
    let one = a / a;

    let mut v: Vec<T> = Vec::new();

    _primes_between(a, b, one, &mut v);

    v
}