自学以太坊智能合约，一知半解之下碰到很多问题，遂记录下，方便以后查找。
第一个智能合约（Faucet）
观看的B站尚硅谷的深入掌握以太坊核心技术-智能合约入门，仿着写个水龙头的智能合约
// Version of Solidity compiler this program was written for
pragma solidity ^0.4.19;
// Our first contract is a faucet!
contract Faucet {
// Give out ether to anyone who asks
function withdraw(uint withdraw_amount) public {
// Limit withdrawal amount
require(withdraw_amount <= 100000000000000000);
// Send the amount to the address that requested it
msg.sender.transfer(withdraw_amount);
}
// Accept any incoming amount
function () public payable {}
}
编译通过：
但是该学习视频已经是两年前的了，用的编译版本比较旧，remix上的例子里，版本都是
// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0
那就试着改一下版本，发现开始报错：
ParserError: Expected a state variable declaration. If you intended this as a fallback function or a function to handle plain ether transactions, use the "fallback" keyword or the "receive" keyword instead.
--> contracts/Faucet.sol:14:32:
|
14 | function () public payable {}
| ^
这是因为在0.6.0的版本更新中
所以我们需要对应下
发现有回退，就要有接收，那就再增加一下receive方法
编译后发现还剩下一个问题，仔细看一下，发现
0.5.0版本中
0.6.0版本中
0.8.0版本中
由此可知，目前msg.sender已经不是address payable了，需要自己另外转一下
编译通过，合约处可以选择Faucet合约了，语法修改完成。
最终改成如下代码：
// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0 <0.9.0;
/**
* @title Faucet
* @dev Our first contract is a faucet!
*/
contract Faucet {
// Give out ether to anyone who asks
function withdraw(uint withdraw_amount) public {
// Limit withdrawal amount
require(withdraw_amount <= 100000000000000000);
// Send the amount to the address that requested it
payable(msg.sender).transfer(withdraw_amount);
}
// Accept any incoming amount
fallback () payable external {}
receive () payable external {}
}