pub struct Service { db: Db, cache: Cache }

impl Service {
    pub fn save(&self, k: &str) { self.db.write(k); }
    pub fn load(&self, k: &str) -> String { self.db.read(k) }
    pub fn put(&self, k: &str) { self.cache.set(k); }
    pub fn evict(&self, k: &str) { self.cache.drop(k); }
}
