将对对象的引用的 vec 存储在另一个数据结构中

Question

编译以下代码时：

pub enum NodeType {
    None,
    Node(Box<Node>),
}

pub struct Node {
    next: NodeType,
}

impl Node {
    fn traverse_recursively<F>(&self, depth: usize, f: &mut F)
    where
        F: FnMut(&Node, usize),
    {
        f(self, depth);

        match &self.next {
            NodeType::None => {}
            NodeType::Node(node) => {
                node.traverse_recursively(depth + 1, f);
            }
        }
    }

    pub fn visit_all<F>(&self, f: &mut F)
    where
        F: FnMut(&Node, usize),
    {
        self.traverse_recursively(1, f);
    }
}

pub fn create_small_recursive_structure() -> Node {
    Node {
        next: NodeType::Node(Box::new(Node {
            next: NodeType::Node(Box::new(Node { next: NodeType::None })),
        })),
    }
}

#[test]
fn test_so() {
    let parent = create_small_recursive_structure();

    let mut visited = Vec::new();

    parent.visit_all(&mut |node, depth| {
        visited.push((node, depth));
    });
}

编译器给我以下错误：

error[E0521]: borrowed data escapes outside of closure
  --> src/so_question.rs:50:9
   |
47 |     let mut visited = Vec::new();
   |         ----------- `visited` declared here, outside of the closure body
48 | 
49 |     parent.visit_all(&mut |node, depth| {
   |                            ---- `node` is a reference that is only valid in the closure body
50 |         visited.push((node, depth));
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ `node` escapes the closure body here

我发现了一个类似的问题，但解决方案对我没有帮助。 IE。我的闭包参数已经没有类型，我已经通过添加和删除类型进行了试验，但似乎没有帮助。

我需要做什么才能临时存储对树结构中节点的引用向量？目的是让向量的寿命比节点结构的寿命短。添加一对额外的括号来为编译器强调这一点没有帮助。

谢谢！

Answer 1

您需要指定生命周期，以便编译器知道引用的生命周期与 self 相同：

pub enum NodeType {
    None,
    Node(Box<Node>),
}

pub struct Node {
    next: NodeType,
}

impl Node {
    fn traverse_recursively<'s, F>(&'s self, depth: usize, f: &mut F)
    where
        F: FnMut(&'s Node, usize),
    {
        f(self, depth);

        match &self.next {
            NodeType::None => {}
            NodeType::Node(node) => {
                node.traverse_recursively(depth + 1, f);
            }
        }
    }

    pub fn visit_all<'s, F>(&'s self, f: &mut F)
    where
        F: FnMut(&'s Node, usize),
    {
        self.traverse_recursively(1, f);
    }
}

pub fn create_small_recursive_structure() -> Node {
    Node {
        next: NodeType::Node(Box::new(Node {
            next: NodeType::Node(Box::new(Node { next: NodeType::None })),
        })),
    }
}


#[test]
fn test_so() {
    let parent = create_small_recursive_structure();

    let mut visited = Vec::new();

    parent.visit_all(&mut |node: &Node, depth| {
        visited.push((node, depth));
    });
}

Playground

将对对象的引用的 vec 存储在另一个数据结构中

Store a vec of references to objects in another data structure

closures

ownership

rust

borrow-checker