Unwrap and access T from an Option>>

Question

I am trying to solve some Leetcode problems with Rust. However, I ran into some difficulties with LeetCode\'s TreeNode implementation.

use std:         


        

Answer 1

Unwrap and access T from an Option<Rc<RefCell<T>>>

You really don't want to try to remove the value from the Option, the Rc or the RefCell via unwrap / try_unwrap / into_inner. Instead, pattern match on the Option and then call borrow on the RefCell to get a reference to the T.

Additionally:

1. Use if let instead of a match statement when you only care about one arm.
2. Variables use snake_case. V is not an appropriate name.
3. There's no need to use a struct here, or to define the helper function publicly. A plain function and a nested function are simpler and exposes less detail.
4. There's no need to provide an explicit type when constructing ret.

pub fn inorder_traversal(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<i32> {
    fn helper(node: &Option<Rc<RefCell<TreeNode>>>, ret: &mut Vec<i32>) {
        if let Some(v) = node {
            let v = v.borrow();

            helper(&v.left, ret);
            ret.push(v.val);
            helper(&v.right, ret);
        }
    }

    let mut ret = vec![];

    if let Some(v) = root {
        helper(&Some(v), &mut ret);
    }

    ret
}

Personally, I'm not a fan of being forced to construct the Some, so I'd probably reorganize the code, which also allows me to stick it as a method on TreeNode:

impl TreeNode {
    pub fn inorder_traversal(&self) -> Vec<i32> {
        fn helper(node: &TreeNode, ret: &mut Vec<i32>) {
            if let Some(ref left) = node.left {
                helper(&left.borrow(), ret);
            }

            ret.push(node.val);

            if let Some(ref right) = node.right {
                helper(&right.borrow(), ret);
            }
        }

        let mut ret = vec![];
        helper(self, &mut ret);
        ret
    }
}

See also:

• Why does Arc::try_unwrap() cause a panic?