//////////////////////////////////////////////////////////////////
// Database part - I have no control over this
//////////////////////////////////////////////////////////////////
struct Database(std::vec::Vec<u8>);
impl Database {
    fn get_txn<'db>(&'db self) -> Transaction<'db> {
        Transaction{
            db: self,
        }
    }
}

struct Transaction<'db> {
    db: &'db Database,
}
impl<'db> Transaction<'db> {
    fn iter(&'db self) -> DatabaseIterator<'db,'db> {
        DatabaseIterator{
            transaction: self,
            iter: self.db.0.iter()
        }
    }
}

struct DatabaseIterator<'txn,'db> {
    transaction: &'txn Transaction<'db>,
    iter: std::slice::Iter<'txn, u8>,
}
impl<'txn,'db> Iterator for DatabaseIterator<'txn,'db> {
    type Item = &'txn u8;

    fn next(&mut self) -> Option<&'txn u8> {
        self.iter.next()
    }
}

//////////////////////////////////////////////////////////////////
// Application part
//////////////////////////////////////////////////////////////////

struct DatabaseBackedObject {
    db: Database,
}
impl DatabaseBackedObject {
    fn iter<'db>(&'db self) -> DatabaseBackedObjectIterator<'db> {
        let txn = self.db.get_txn();
        DatabaseBackedObjectIterator {
            txn,
            iter: txn.iter(),
        }
    }
}

struct DatabaseBackedObjectIterator<'dbo> {
    txn: Transaction<'dbo>,
    iter: DatabaseIterator<'dbo,'dbo>,
}
impl<'dbo> Iterator for DatabaseBackedObjectIterator<'dbo> {
    type Item = &'dbo u8;
    fn next(&mut self) -> Option<&'dbo u8> {
        self.iter.next()
    }
}



fn main() {
    let db = Database(vec![1,2,3]);
    let dbo = DatabaseBackedObject{db};
    for x in dbo.iter() {
        println!("{}", x);
    }
}