📝 第06课：Solidity基础

智能合约 ✅ 验证通过

📖 一、Solidity语言概览

Solidity = 以太坊智能合约的官方语言，由Gavin Wood提出，Christian Reitwiessner主导开发。它是静态类型、面向合约的高级语言，编译后运行在EVM上。

📖 二、合约结构详解

2.1 SPDX许可证与版本约束

💻 三、代码实战：第一个智能合约

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

/// @title 计数器合约 - Solidity基础完整示例
/// @author Web3课程
/// @notice 实现计数、权限管理、ETH接收功能
contract Counter {
    // ===== 状态变量 =====
    uint256 private _count;
    address public owner;
    uint256 public lastModified;
    uint256 public totalDeposits;

    // ===== 事件 =====
    event CountIncremented(uint256 newCount, address indexed caller);
    event CountDecremented(uint256 newCount, address indexed caller);
    event CountReset(address indexed caller);
    event OwnershipTransferred(address indexed oldOwner, address indexed newOwner);
    event DepositReceived(address indexed from, uint256 amount);

    // ===== 自定义错误 =====
    error Unauthorized(address caller, address required);
    error CountAlreadyZero();
    error ZeroAddress();

    // ===== 修饰符 =====
    modifier onlyOwner() {
        if (msg.sender != owner) {
            revert Unauthorized(msg.sender, owner);
        }
        _;
    }

    modifier countNotZero() {
        if (_count == 0) revert CountAlreadyZero();
        _;
    }

    // ===== 构造函数 =====
    constructor() {
        owner = msg.sender;
        _count = 0;
        lastModified = block.timestamp;
    }

    // ===== 读函数 (view - 不消耗Gas) =====
    function getCount() public view returns (uint256) {
        return _count;
    }

    function getContractBalance() public view returns (uint256) {
        return address(this).balance;
    }

    function getTimeSinceLastModify() public view returns (uint256) {
        return block.timestamp - lastModified;
    }

    // ===== 写函数 (消耗Gas) =====
    function increment() public {
        _count += 1;
        lastModified = block.timestamp;
        emit CountIncremented(_count, msg.sender);
    }

    function decrement() public countNotZero {
        _count -= 1;
        lastModified = block.timestamp;
        emit CountDecremented(_count, msg.sender);
    }

    function reset() public onlyOwner {
        _count = 0;
        lastModified = block.timestamp;
        emit CountReset(msg.sender);
    }

    function batchIncrement(uint256 times) public {
        require(times > 0 && times <= 100, "Times must be 1-100");
        for (uint256 i = 0; i < times; i++) {
            _count += 1;
        }
        lastModified = block.timestamp;
        emit CountIncremented(_count, msg.sender);
    }

    // ===== 特殊函数 =====
    function transferOwnership(address newOwner) public onlyOwner {
        if (newOwner == address(0)) revert ZeroAddress();
        address oldOwner = owner;
        owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }

    // ===== 接收ETH =====
    receive() external payable {
        totalDeposits += msg.value;
        emit DepositReceived(msg.sender, msg.value);
    }

    fallback() external payable {
        totalDeposits += msg.value;
    }

    // ===== 提取函数 =====
    function withdraw() public onlyOwner {
        uint256 balance = address(this).balance;
        (bool success, ) = payable(owner).call{value: balance}("");
        require(success, "Withdrawal failed");
    }
}
// ✅ 验证通过 - Remix IDE编译部署测试

📖 四、函数可见性详解

📖 五、状态可变性

📖 六、数据位置初探

📝 七、练习题

🔧 八、动手实验