How to handle `<Option<Box<_>>>` in Rust?

The code:

pub struct Scope<'a> {
    pub parent: Option<Box<Scope<'a>>>,
    pub vars: HashMap<&'a str, Value>,
}

impl<'a> Scope<'a> {
    pub fn get(&self, name: &str) -> Result<&Value, String> {
        if let Some(v) = self.vars.get(name) {
            Ok(v)
        } else if let Some(parent) = self.parent { // <- error here
            parent.get(name) // <- and here
        } else {
            Err(format!("{} is undefined", name))
        }
    }
}

And the compiler gives me this error:

error[E0507]: cannot move out of `self.parent` as enum variant `Some` which is behind a shared reference
  --> src/interpreter/scope.rs:13:38
   |
13 |         } else if let Some(parent) = self.parent {
   |                            ------    ^^^^^^^^^^^ help: consider borrowing here: `&self.parent`
   |                            |
   |                            data moved here
   |                            move occurs because `parent` has type `Box<scope::Scope<'_>>`, which does not implement the `Copy` trait

error[E0515]: cannot return reference to local data `*parent`
  --> src/interpreter/scope.rs:14:13
   |
14 |             parent.get(name)
   |             ^^^^^^^^^^^^^^^^ returns a reference to data owned by the current function

I have no idea how to fix this error. How can I fix this?

Thanks in advance.

>Solution :

You are transfering the ownership of the value inside self.parent. By doing let Some(parent) = self.parent now the value that was on self.parent is owned by parent. This would cause self.parent to be undefined because there can only be one owner at a time, hence the compilation error.

See ownership rules on the rust book

You can instead borrow self.parent as suggested:

impl<'a> Scope<'a> {
    pub fn get(&self, name: &str) -> Result<&Value, String> {
        if let Some(v) = self.vars.get(name) {
            Ok(v)
        } else if let Some(parent) = &self.parent { // <- borrowing self.parent
            parent.get(name) // <- and here
        } else {
            Err(format!("{} is undefined", name))
        }
    }
}