# Solidity进阶实战

By [Benson](https://paragraph.com/@bensonxu) · 2023-09-02

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1.逐行解读PEPE合约
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    // SPDX-License-Identifier: MIT
    pragma solidity ^0.8.0;
    
    abstract contract Context {
        function _msgSender() internal view virtual returns (address) {
            return msg.sender;
        }
    
        function _msgData() internal view virtual returns (bytes calldata) {
            return msg.data;
        }
    }
    
    abstract contract Ownable is Context {
        address private _owner;
    
        event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
    
        constructor() {
            _transferOwnership(_msgSender());
        }
    
        function owner() public view virtual returns (address) {
            return _owner;
        }
    
        modifier onlyOwner() {
            require(owner() == _msgSender(), "Ownable: caller is not the owner");
            _;
        }
    
        function renounceOwnership() public virtual onlyOwner {
            _transferOwnership(address(0));
        }
    
        function transferOwnership(address newOwner) public virtual onlyOwner {
            require(newOwner != address(0), "Ownable: new owner is the zero address");
            _transferOwnership(newOwner);
        }
    
        function _transferOwnership(address newOwner) internal virtual {
            address oldOwner = _owner;
            _owner = newOwner;
            emit OwnershipTransferred(oldOwner, newOwner);
        }
    }
    
    interface IERC20 {
    
        function totalSupply() external view returns (uint256);
        function balanceOf(address account) external view returns (uint256);
        function transfer(address recipient, uint256 amount) external returns (bool);
        function allowance(address owner, address spender) external view returns (uint256);
        function approve(address spender, uint256 amount) external returns (bool);
        function transferFrom(
            address sender,
            address recipient,
            uint256 amount
        ) external returns (bool);
    
        event Transfer(address indexed from, address indexed to, uint256 value);
        event Approval(address indexed owner, address indexed spender, uint256 value);
    }
    
    interface IERC20Metadata is IERC20 {
        function name() external view returns (string memory);
        function symbol() external view returns (string memory);
        function decimals() external view returns (uint8);
    }
    
    contract ERC20 is Context, IERC20, IERC20Metadata {
        mapping(address => uint256) private _balances; // 代币余额
        mapping(address => mapping(address => uint256)) private _allowances; // 代币授权额度
    
        uint256 private _totalSupply; // 总量
        string private _name; // 代币名称
        string private _symbol; // 代币缩写
    
        // 初始化 代币名称 代币缩写
        constructor(string memory name_, string memory symbol_) {
            _name = name_;
            _symbol = symbol_;
        }
    
        // 取读 代币名称 
        function name() public view virtual override returns (string memory) {
            return _name;
        }
    
        // 取读 代币缩写
        function symbol() public view virtual override returns (string memory) {
            return _symbol;
        }
    
        // 取读 代币精度
        function decimals() public view virtual override returns (uint8) {
            return 18;
        }
    
        // 取读 代币总量
        function totalSupply() public view virtual override returns (uint256) {
            return _totalSupply;
        }
    
        // 取读 某一地址代币余额
        function balanceOf(address account) public view virtual override returns (uint256) {
            return _balances[account];
        }
    
        // 写入 转账
        function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
            _transfer(_msgSender(), recipient, amount);
            return true; 
        }
    
        // 取读 某一地址授权额度
        function allowance(address owner, address spender) public view virtual override returns (uint256) {
            return _allowances[owner][spender];
        }
    
        // 写入 某一地址授权额度
        function approve(address spender, uint256 amount) public virtual override returns (bool) {
            _approve(_msgSender(), spender, amount);
            return true;
        }
    
        // 写入 转账
        function transferFrom(
            address sender,
            address recipient,
            uint256 amount
        ) public virtual override returns (bool) {
            _transfer(sender, recipient, amount);
            uint256 currentAllowance = _allowances[sender][_msgSender()];
            require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
            unchecked {
                _approve(sender, _msgSender(), currentAllowance - amount);
            }
            return true;
        }
    
        // 写入 增加授权额度
        function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
            _approve(_msgSender(), spender, _allowances[_msgSender()][spender] + addedValue);
            return true;
        }
    
        // 写入 减少授权额度
        function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
            uint256 currentAllowance = _allowances[_msgSender()][spender];
            require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
            unchecked {
                _approve(_msgSender(), spender, currentAllowance - subtractedValue);
            }
            return true;
        }
        
        // 写入 转账
        function _transfer(
            address sender,
            address recipient,
            uint256 amount
        ) internal virtual {
            require(sender != address(0), "ERC20: transfer from the zero address");
            require(recipient != address(0), "ERC20: transfer to the zero address");
    
            _beforeTokenTransfer(sender, recipient, amount);
    
            uint256 senderBalance = _balances[sender];
            require(senderBalance >= amount, "ERC20: transfer amount exceeds balance");
            unchecked {
                _balances[sender] = senderBalance - amount; // 100 - 100
            }
            _balances[recipient] += amount; // 0 + 100
            emit Transfer(sender, recipient, amount);
    
            _afterTokenTransfer(sender, recipient, amount);
        }
    
        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);
    
            _afterTokenTransfer(address(0), account, amount);
        }
    
        function _burn(address account, uint256 amount) internal virtual {
            require(account != address(0), "ERC20: burn from the zero address");
    
            _beforeTokenTransfer(account, address(0), amount);
    
            uint256 accountBalance = _balances[account];
            require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
            unchecked {
                _balances[account] = accountBalance - amount;
            }
            _totalSupply -= amount;
            emit Transfer(account, address(0), amount);
    
            _afterTokenTransfer(account, address(0), amount);
        }
    
    
        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);
        }
    
        function _beforeTokenTransfer(
            address from,
            address to,
            uint256 amount
        ) internal virtual {}
    
        function _afterTokenTransfer(
            address from,
            address to,
            uint256 amount
        ) internal virtual {}
    }
    
    contract PepeToken is Ownable, ERC20 {
        bool public limited;
        uint256 public maxHoldingAmount;
        uint256 public minHoldingAmount;
        address public uniswapV2Pair; // V2交易对
        mapping(address => bool) public blacklists; // 黑名单
    
        constructor(uint256 _totalSupply) ERC20("Pepe", "PEPE") {
            _mint(msg.sender, _totalSupply);
        }
        
        // 写入 黑名单
        function blacklist(address _address, bool _isBlacklisting) external onlyOwner {
            blacklists[_address] = _isBlacklisting;
        }
    
        // 写入 交易规则
        function setRule(bool _limited, address _uniswapV2Pair, uint256 _maxHoldingAmount, uint256 _minHoldingAmount) external onlyOwner {
            limited = _limited;
            uniswapV2Pair = _uniswapV2Pair;
            maxHoldingAmount = _maxHoldingAmount;
            minHoldingAmount = _minHoldingAmount;
        }
    
        // 交易前
        function _beforeTokenTransfer(
            address from,
            address to,
            uint256 amount
        ) override internal virtual {
            //黑名单限制
            require(!blacklists[to] && !blacklists[from], "Blacklisted");
    
            // 交易是否开始限制
            if (uniswapV2Pair == address(0)) {
                require(from == owner() || to == owner(), "trading is not started");
                return;
            }
    
            // 钱包数量限制
            if (limited && from == uniswapV2Pair) {
                require(super.balanceOf(to) + amount <= maxHoldingAmount && super.balanceOf(to) + amount >= minHoldingAmount, "Forbid");
            }
        }
    
        // 销毁
        function burn(uint256 value) external {
            _burn(msg.sender, value);
        }
    }

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*Originally published on [Benson](https://paragraph.com/@bensonxu/solidity-2)*