contract StateVariableExample {
    // 公共狀態(tài)變量
    uint256 public totalSupply;
    // 私有狀態(tài)變量
    address private owner;
    // 常量狀態(tài)變量
    uint256 constant public DECIMALS = 18;
    // 不可變狀態(tài)變量
    address immutable public CREATOR;
    constructor() {
        CREATOR = msg.sender;
    }
}

contract LocalVariableExample {
    function calculate() public pure returns (uint) {
        // 局部變量，僅在函數(shù)內(nèi)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;    // 當(dāng)前區(qū)塊號(hào)
        timestamp = block.timestamp;    // 當(dāng)前區(qū)塊時(shí)間戳
        sender = msg.sender;           // 調(diào)用者地址
    }
}

contract VisibilityExample {
    uint256 public publicVar;      // 自動(dòng)生成getter函數(shù)
    uint256 private privateVar;    // 僅合約內(nèi)部可訪問(wèn)
    uint256 internal internalVar;  // 可被繼承合約訪問(wèn)
    function getPrivateVar() public view returns (uint256) {
        return privateVar;  // 通過(guò)公共函數(shù)訪問(wèn)私有變量
    }
}

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的復(fù)制
        newData.numbers = _data.numbers;
        newData.text = _data.text;
    }
}

contract MappingExample {
    // 簡(jiǎn)單映射
    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 {
    // 未優(yōu)化: 使用3個(gè)存儲(chǔ)槽
    uint128 a;    // 槽1
    uint256 b;    // 槽2
    uint128 c;    // 槽3
    // 優(yōu)化后: 使用2個(gè)存儲(chǔ)槽
    uint128 a;    // 槽1
    uint128 c;    // 槽1
    uint256 b;    // 槽2
}

contract ConstantExample {
    // 編譯時(shí)常量，不占用存儲(chǔ)
    uint256 constant public MAX_SUPPLY = 1000000 * (10 ** 18);
    // 部署時(shí)固定，僅占用代碼空間
    address immutable public TREASURY;
    constructor(address _treasury) {
        TREASURY = _treasury;
    }
}