注：本教程为技术教程，不谈论且不涉及炒作任何数字货币
// SPDX-License-Identifier: MIT pragma solidity ^0.8.0; import "./IERC20.sol"; import "./extensions/IERC20Metadata.sol"; import "../../utils/Context.sol"; /** * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226 *allowance：消费限额 * */ contract ERC20 is Context, IERC20, IERC20Metadata { //定义了一个合约叫ERC20，is“继承” //address是地址类型 mapping(address => uint256) private _balances; //address在_balance在字典里映射256位一个值，仅当前合约可见； //【这里要修改】 字典是不是balance mapping(address => mapping(address => uint256)) private _allowances; //这里是一个嵌套，从外到里看，首先address映射到另外一个小mapping中，其次小mapping运算后得出一个256位的值， //所以，大mapping得出一个256位的值 uint256 private _totalSupply; string private _name; string private _symbol; /** * 设置name symbol *decimals翻译为小数，这里理解为精度，默认是18位，只设置一次 *constructor构造函数，部署运行且只运行一次，构造了2个临时的变量；（初始化） *storage变量是永久的，memory是临时的、当外部函数对某合约调用完成时，内存型变量即被移除。 */ constructor(string memory name_, string memory symbol_) { _name = name_; _symbol = symbol_; } /** * 返回标记的名称 * */ function name() public view virtual override returns (string memory) { return _name; } /** * @dev返回代币的名字，一般是缩写？？？ * */ function symbol() public view virtual override returns (string memory) { return _symbol; } /** *显示这个数的“精度”，例如如果是2，505则表示5.05 */ function decimals() public view virtual override returns (uint8) { return 18; } /** *_totalSupply是代币总量。 */ function totalSupply() public view virtual override returns (uint256) { return _totalSupply; } /** * 返回账户余额 */ function balanceOf(address account) public view virtual override returns (uint256) { return _balances[account];//这个_balances是参数 } /** * Requirements: *接收者的地址不为空，调用者要有额度 */ function transfer(address recipient, uint256 amount) public virtual override returns (bool) { _transfer(_msgSender(), recipient, amount); return true; } /** * @dev See {IERC20-allowance}. */ function allowance(address owner, address spender) public virtual override returns (uint256) { // allowance理解为“转移”；view是修饰符的函数，查看某种状态，在接下来的调用函数不会消耗gas; // virtual继承 override函数重写 //父合约标记为 virtual 函数可以在继承合约里重写(overridden)以更改他们的行为。 //重写的函数需要使用关键字 override 修饰。 return _allowances[owner][spender]; } /** * Requirements: * - `spender` cannot be the zero address. *把approve理解为授权，用户1授权spender有amount的额度。 */ function approve(address spender, uint256 amount) public virtual override returns (bool) { _approve(_msgSender(), spender, amount); return true; } /** * Requirements: * 发送者和接收者地址不为空 * 发送者要有钱 * 调用者要有额度（有发送者授权的额度） */ function transferFrom( address sender, address recipient, uint256 amount ) public virtual override returns (bool) { _transfer(sender, recipient, amount); uint256 currentAllowance = _allowances[sender][_msgSender()]; //看上面的allowance，是两次mapping得出的是一个数，而这个数就是两者的关系。 require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance"); //进行一个比较，比较 当前额度>=待转出的数值，如果成立则输出：。。。。 unchecked { _approve(sender, _msgSender(), currentAllowance - amount); } //？？？？这是不检查吗？【忽略】 return true; } /** * increase和decrease allowance */ function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) { //增加权限 _approve(_msgSender(), spender, _allowances[_msgSender()][spender] + addedValue); //因为是映射，所以得出两者相关的值，比如已经授权给B多少了，这个值就是初始值。加上刚刚输入的权限值，就为最终结果。 return true; } function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) { uint256 currentAllowance = _allowances[_msgSender()][spender]; require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero"); //当前额度>=减去额度,则显示：减少授权额度到零？？？ unchecked { _approve(_msgSender(), spender, currentAllowance - subtractedValue); } return true; } /** * @dev Moves `amount` of tokens from `sender` to `recipient`. * * This internal function is equivalent to {transfer}, and can be used to * e.g. implement automatic token fees, slashing mechanisms, etc. * * Emits a {Transfer} event. * * Requirements: * * - `sender` cannot be the zero address. * - `recipient` cannot be the zero address. * - `sender` must have a balance of at least `amount`. */ function _transfer( address sender, address recipient, uint256 amount ) internal virtual { require(sender != address(0), "ERC20: transfer from the zero address"); //发送者地址不为空，显示传递者为空 require(recipient != address(0), "ERC20: transfer to the zero address"); //接收者不为空 _beforeTokenTransfer(sender, recipient, amount); uint256 senderBalance = _balances[sender]; //什么意思啊 require(senderBalance >= amount, "ERC20: transfer amount exceeds balance"); //超过平衡 unchecked { _balances[sender] = senderBalance - amount; } _balances[recipient] += amount; emit Transfer(sender, recipient, amount); //触发一个事件用emit说明，这里触发Transfer事件 。。。。不显示，为了让前端找结果 _afterTokenTransfer(sender, recipient, amount); //这句话的语法不太懂 } /** @dev Creates `amount` tokens and assigns them to `account`, increasing * the total supply. * * Emits a {Transfer} event with `from` set to the zero address. * * Requirements: * * - `account` cannot be the zero address. */ function _mint(address account, uint256 amount) internal virtual { require(account != address(0), "ERC20: mint to the zero address"); _beforeTokenTransfer(address(0), account, amount); _totalSupply += amount; _balances[account] += amount; emit Transfer(address(0), account, amount);//0--x是挖矿 _afterTokenTransfer(address(0), account, amount); } /** * @dev Destroys `amount` tokens from `account`, reducing the * total supply. *销毁 */ function _burn(address account, uint256 amount) internal virtual { require(account != address(0), "ERC20: burn from the zero address");//x--0是铸币 _beforeTokenTransfer(account, address(0), amount); uint256 accountBalance = _balances[account]; require(accountBalance >= amount, "ERC20: burn amount exceeds balance（超过平衡）"); unchecked { _balances[account] = accountBalance - amount; } _totalSupply -= amount; emit Transfer(account, address(0), amount); _afterTokenTransfer(account, address(0), amount); } /** * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens. * * This internal function is equivalent to `approve`, and can be used to * e.g. set automatic allowances for certain subsystems, etc. * * Emits an {Approval} event. * * Requirements: * * - `owner` cannot be the zero address. * - `spender` cannot be the zero address. */ function _approve(address owner,address spender,uint256 amount) internal virtual { require(owner != address(0), "ERC20: approve from the zero address"); require(spender != address(0), "ERC20: approve to the zero address"); _allowances[owner][spender] = amount; emit Approval(owner, spender, amount); } /** * @dev Hook that is called before any transfer of tokens. This includes * minting and burning. * * Calling conditions: * * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens * will be transferred to `to`. * - when `from` is zero, `amount` tokens will be minted for `to`. * - when `to` is zero, `amount` of ``from``'s tokens will be burned. * - `from` and `to` are never both zero. * * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks]. */ function _beforeTokenTransfer(address from,address to,uint256 amount) internal virtual {} function _afterTokenTransfer( address from, address to, uint256 amount ) internal virtual {} }