18.Constructor

Constructor

一个特殊的方法，在合约部署的时候调用，而且只调用这一次

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.1;

// Base contract X
contract X {
    address public owner;
    uint256 public x;

    constructor(uint256 _x) {
        owner = msg.sender;
        x = _x;
    }
}

案例

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.1;

// Base contract X
contract Ownable {
    address public owner;

    constructor() {
        owner = msg.sender;
    }

    // 创建function modifier， 只有owner才能call function
    modifier onlyOwner() {
        require(msg.sender == owner, "not owner");
        _;
    }

    function setOwner(address _newOwner) external onlyOwner {
        require(_newOwner != address(0), "invalid address");
        owner = _newOwner;
    }

    function onlyOwnerCanCallThisFunc() external onlyOwner {
        //
    }

    function anyOneCanCall() external {}
}

案例

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.1;

// Base contract X
contract X {
    string public name;

    constructor(string memory _name) {
        name = _name;
    }
}

// Base contract Y
contract Y {
    string public text;

    constructor(string memory _text) {
        text = _text;
    }
}

// There are 2 ways to initialize parent contract with parameters.

// Pass the parameters here in the inheritance list.
contract B is X("Input to X"), Y("Input to Y") {

}

contract C is X, Y {
    // Pass the parameters here in the constructor,
    // similar to function modifiers.
    constructor(string memory _name, string memory _text) X(_name) Y(_text) {}
}

// Parent constructors are always called in the order of inheritance
// regardless of the order of parent contracts listed in the
// constructor of the child contract.

// Order of constructors called:
// 1. X
// 2. Y
// 3. D
contract D is X, Y {
    constructor() X("X was called") Y("Y was called") {}
}

// Order of constructors called:
// 1. X
// 2. Y
// 3. E
contract E is X, Y {
    constructor() Y("Y was called") X("X was called") {}
}