use std::borrow::Cow;
use std::collections::HashMap;

#[derive(Clone, Debug)]
struct Node {
    data: Vec<u8>,
}

struct Db;

impl Db {
    fn get(&self, key: &str) -> Node {
        Node { data: key.as_bytes().to_vec() }
    }
}

fn main() {
    let valid = "this-is-rust";
    let invalid = "something-else";

    let db = Db;
    let mut cache = HashMap::new();
    cache.insert(valid.clone(), Node { data: vec![0; 2] });

    {
        let key = valid;
        let node: Cow<Node> = match cache.get(key) {
            Some(node) => Cow::Borrowed(node),
            None => Cow::Owned(db.get(key)),
        };
        println!("Cached Data: {:?}", node);
    }

    {
        let key = invalid;
        let node: Cow<Node> = match cache.get(key) {
            Some(node) => Cow::Borrowed(node),
            None => Cow::Owned(db.get(key)),
        };
        println!("Uncached Data: {:?}", node);
    }
}