The selfdestruct() function has an interesting feature as it enables us to reduce the cost of the destruction transaction. It's based on the SUICIDE opcode, which uses negative gas because the operation frees up space on the blockchain by clearing all of the contract's state data. This negative gas is deducted from the total gas cost of the transaction, therefore reducing your gas cost. In our case, this method costs 14,211 gas, less than a normal transfer (which costs 21,000 gas):
