Method new

chapter 4/blockchain.rs:242–247

(tip_hash: String, db: Db)

impl BlockchainIterator {
    fn new(tip_hash: String, db: Db) -> BlockchainIterator {
        BlockchainIterator {
            current_hash: tip_hash,
            db,
        }
    }

    pub fn next(&mut self) -> Option<Block> {
        let block_tree = self.db.open_tree(BLOCKS_TREE).unwrap();