bindings_box.rs

// while iterating, have a `mut bindings: Vec<Bindings>`
// have a structure of Scopes that contain references to values in `bindings`
// a Binding doesn't refer to a Scope
// at the end, return `bindings`, so Scopes cannot own anything in bindings

// mutable reference is a subtype of immutable reference
fn example<'source>(
    bindings: &mut Vec<Box<Binding<'source>>>,
    names: Vec<&'source str>,
) {
    let mut scope: Scope<'source> = Scope { bindings: vec![] };
    for name in names.into_iter() {
        let binding: Binding<'source> = Binding { name };

        // borrowed mutably
        bindings.push(Box::new(binding));

        // so, can't borrow immutably here
        let binding_ref: Box<Binding<'source>> = bindings.last().unwrap().clone();
        scope.bindings.push(binding_ref);
    }
}

#[derive(Debug, Clone)]
struct Binding<'source> {
    name: &'source str,
}

#[derive(Debug, Clone)]
struct Scope<'source> {
    pub bindings: Vec<Box<Binding<'source>>>,
}

fn main() {}