Solidity 变量详解之类型、作用域与最佳实践记录

contract StateVariableExample {
    // 公共状态变量
    uint256 public totalSupply;
    // 私有状态变量
    address private owner;
    // 常量状态变量
    uint256 constant public DECIMALS = 18;
    // 不可变状态变量
    address immutable public CREATOR;
    constructor() {
        CREATOR = msg.sender;
    }
}

contract LocalVariableExample {
    function calculate() public pure returns (uint) {
        // 局部变量，仅在函数内有效
        uint256 a = 1;
        uint256 b = 2;
        uint256 result = a + b;
        return result;
    }
}

contract GlobalVariableExample {
    function getBlockInfo() public view returns (
        uint256 blockNumber,
        uint256 timestamp,
        address sender
    ) {
        blockNumber = block.number;    // 当前区块号
        timestamp = block.timestamp;    // 当前区块时间戳
        sender = msg.sender;           // 调用者地址
    }
}

contract VisibilityExample {
    uint256 public publicVar;      // 自动生成getter函数
    uint256 private privateVar;    // 仅合约内部可访问
    uint256 internal internalVar;  // 可被继承合约访问
    function getPrivateVar() public view returns (uint256) {
        return privateVar;  // 通过公共函数访问私有变量
    }
}

contract StorageExample {
    struct Data {
        uint256[] numbers;
        string text;
    }
    Data[] public dataArray;
    function processData(Data memory _data) public {
        // storage引用
        Data storage newData = dataArray.push();
        // memory到storage的复制
        newData.numbers = _data.numbers;
        newData.text = _data.text;
    }
}

contract MappingExample {
    // 简单映射
    mapping(address => uint256) public balances;
    // 嵌套映射
    mapping(address => mapping(address => bool)) public approvals;
    function updateBalance(uint256 _amount) public {
        balances[msg.sender] = _amount;
    }
    function approve(address _spender) public {
        approvals[msg.sender][_spender] = true;
    }
}

contract EnumExample {
    enum Status { Pending, Active, Inactive }
    Status public currentStatus;
    function setStatus(Status _status) public {
        currentStatus = _status;
    }
    function isActive() public view returns (bool) {
        return currentStatus == Status.Active;
    }
}

contract StorageOptimization {
    // 未优化: 使用3个存储槽
    uint128 a;    // 槽1
    uint256 b;    // 槽2
    uint128 c;    // 槽3
    // 优化后: 使用2个存储槽
    uint128 a;    // 槽1
    uint128 c;    // 槽1
    uint256 b;    // 槽2
}

contract ConstantExample {
    // 编译时常量，不占用存储
    uint256 constant public MAX_SUPPLY = 1000000 * (10 ** 18);
    // 部署时固定，仅占用代码空间
    address immutable public TREASURY;
    constructor(address _treasury) {
        TREASURY = _treasury;
    }
}