Cannot move out of borrowed content when matching an enum

Question

I\'m trying to print out a tree (it\'s a LinkedList right now, but that will be fixed):

use std::io;
use std::rc::Rc;

enum NodeKind {
    Branc         


        

Answer 1

The error is displayed because by default match will perform a move.

After a value is moved (i.e. wasn't taken by reference or method that takes self was called) subsequent calls fail. You'll probably need to clone, which is a property both of your struct and enum lack. Once you add those (#[derive(Clone)) and change current = *next; into current = (*next).clone();, your program will work again!

use std::io;
use std::rc::Rc;

#[derive(Clone)]
enum NodeKind {
    Branch(Rc),
    Leaf,
}

#[derive(Clone)]
struct Node {
    value: i32,
    kind: NodeKind,
}

fn main() {
    let leaf = Node { value: 10, kind: NodeKind::Leaf };
    let branch = Node { value: 50, kind: NodeKind::Branch(std::rc::Rc::new(leaf)) };
    let root = Node { value: 100, kind: NodeKind::Branch(std::rc::Rc::new(branch)) };

    let mut current = root;
    while true {
        println!("{}", current.value);
        match current.kind {
            NodeKind::Branch(next) => {
                current = (*next).clone();
            }
            NodeKind::Leaf => {
                break;
            }
        }
    }

    let reader = io::stdin();
    let buff = &mut String::new();
    let read = reader.read_line(buff);
}

Playground

If you let mut current = &root then you can avoid clone() as per Vladimir's response below (playpen of Vladimir's version).