revert

If a require condition fails, the transaction reverts and all state changes are undone.如果 require 条件未通过，交易将会回滚，并且所有状态更改都会被撤销。

A failed transaction still consumes gas, even though the state reverts to its original value.即使状态回滚到了原始值，失败的交易仍然会消耗 gas。