Method write_tail

code/chapter09/blockchain/blockchain5/core/src/blockchain.rs:62–66

(mut db: &mut Database<BKey>, block: &Block)

    }

    fn write_tail(mut db: &mut Database<BKey>, block: &Block) {
        let key = BKey{ val: U256::from("tail".as_bytes()) };
        let val = serialize(&(block.hash));
        BlockChainDb::write_db(&mut db, key, &val);
    }

    pub fn block_info(&self) {
        for b in self.blocks.iter() {