为什么在Openzeppelin的可初始化契约中使用_initializing和isTopLevelCall变量？

Question

这是代理模式上下文中的抽象契约：

abstract contract Initializable {
    bool private _initialized;
    bool private _initializing;

    modifier initializer() {
        require(_initializing || !_initialized, "Initializable: contract is already initialized");

        bool isTopLevelCall = !_initializing;
        if (isTopLevelCall) {
            _initializing = true;
            _initialized = true;
        }

        _;

        if (isTopLevelCall) {
            _initializing = false;
        }
    }
}

contract UpgradebleTest1 is Initializable {
    uint public x;

    function initialize(uint _x) public initializer {
        x = _x;
    }
}

我不明白_initializing和isTopLevelCall的必要性。仅仅使用_initialized进行控制还不够吗？

谢谢,

Answer 1

_initializing和isTopLevelCall组合允许使用initializer修饰符进行链接调用：

contract UpgradebleTest1 is Initializable {
    uint public x;

    function initialize(uint _x) public initializer {
        internalInit(_x);
    }

    function internalInit(uint _x) internal initializer {
        x = _x;
    }
}

如果没有_initializing和isTopLevelCall检查，initializer修饰符将传递第一个调用(initialize())，但在第二个调用(internalInit())上失败。

modifier initializer() {
    require(!_initialized, "Initializable: contract is already initialized");
    _initialized = true;
}

Answer 2

abstract contract Initializable {
        bool private _initialized;
    
        modifier initializer() {
            require(!_initialized, "Initializable: co...");
            _;
            _initialized = true;
        }
    }
    
contract UpgradebleTestParent is Initializable {
    uint public x;

    function initialize(uint _x) internal initializer {
        x = _x;
    }
}

contract UpgradebleTestMain is UpgradebleTestParent {
    function init(uint _x) public initializer {
        initialize(_x);
    }
}

如果如上，它将执行相同的逻辑，但是_initialized = true；将不必要地执行两次，对吗？然而，它似乎比前一个更便宜的一个变量和相关的附加指令？难到不是么？