如何从可变向量中克隆最后一个元素，然后将值推送到 Rust 中的向量？

Question

如何从 mutable 向量中克隆最后一个元素，然后将值推送到 Rust 中的向量？

fn ElementsFromPoint(&self, ...) -> Vec<Root<Element>> {

    let mut elements: Vec<Root<Element>> = self.elements_from_point(point).iter()
        .map(|&untrusted_node_addr| {...}).collect();     

    let last_element = elements.last().clone().unwrap(); // elements.last() is Option<&Root<Element>>
    if let Some(root_element) = self.GetDocumentElement() { //self.GetDocumentElement() is Option<Root<Element>>
        if *last_element != root_element {
            elements.push(root_element);
        }
    }


    elements
}

错误是

2620:17: 2620:25 error: cannot borrow `elements` as mutable because it is also borrowed as immutable [E0502]
2620                 elements.push(root_element);
                     ^~~~~~~~
2617:28: 2617:36 note: previous borrow of `elements` occurs here; the immutable borrow prevents subsequent moves or mutable borrows of `elements` until the borrow ends
2617         let last_element = elements.last().clone().unwrap();
                                ^~~~~~~~
2626:6: 2626:6 note: previous borrow ends here
2590     fn ElementsFromPoint(&self, x: Finite<f64>, y: Finite<f64>) -> Vec<Root<Element>> {
                                                         ...
2626     }
                                                             ^
2625:9: 2625:17 error: cannot move out of `elements` because it is borrowed [E0505]
2625         elements
             ^~~~~~~~
2617:28: 2617:36 note: borrow of `elements` occurs here
2617         let last_element = elements.last().clone().unwrap();

我已阅读this 并尝试过

let last_element = elements.last().unwrap().clone();

还有

let last_element = elements.last().map(|t| t.clone()).unwrap();

但还是失败了。

还没有为Root<T> 实现.cloned()。

有没有办法从 mutable 向量中克隆最后一个元素，然后将值推送到 Rust 中的向量？还是应该先实现Cloned trait？

Answer 1

试试这个

fn ElementsFromPoint(&self, ...) -> Vec<Root<Element>> {

    let mut elements: Vec<Root<Element>> = self.elements_from_point(point).iter()
        .map(|&untrusted_node_addr| {...}).collect();


    if let Some(root_element) = self.GetDocumentElement() {
        if {
            match elements.last() {
                Some(last_element) => *last_element != root_element,
                None => true
            }                
        } {
            elements.push(root_element);
        }
    }

    elements
}