Solidity - contract inheritance sub contract contains constructor errors and one contract calls the view function of another contract to charge gas fees

When the contract inherits the sub contract and contains a constructor, an error occurs

error message

When writing a business contract , An error occurs when the inherited contract contains a constructor , Remove the constructor from the inherited contract , Some strange , So write a simple example to reproduce , The contract code is as follows ：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

// Base contract interface 
interface IcontractA {
    function getMsg() external view returns(string memory);
}

// Base contract implementation 
contract contractA is IcontractA {
    string message;

    // Constructors 
    constructor(string memory _message) {
        message = _message;
    }

    function _getMsg() internal view returns (string memory) {
        return message;
    }

    function getMsg() external override view returns(string memory) {
        return _getMsg();
    }
}

// Sub contract  -  Inheritance base contract 
contract contractB is contractA {
    address admin;

    // Constructors 
    constructor(string memory _message) {
        admin = msg.sender;
    }

    // Call the base contract function 
    function callA() external view returns(string memory) {
        return _getMsg();
    }
}

error message

TypeError: Contract "contractB" should be marked as abstract. --> Test/CallContract.sol:28:1: | 28 | contract contractB is contractA { | ^ (Relevant source part starts here and spans across multiple lines). Note: Missing implementation: --> Test/CallContract.sol:14:5: | 14 | constructor(string memory _message) { | ^ (Relevant source part starts here and spans across multiple lines).

Remix Browser execution results ：

reason

When the contract is inherited , Derivative contracts （ Sub contract ） You need to provide all the parameters required by the base class constructor , See   contract — Solidity develop file

Solution

Add the parameters required by the base contract in the derived contract constructor

32 The adjustment is as follows ：

constructor(string memory _message) contractA(_message) {

The revised contract code is as follows ：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

// Base contract interface 
interface IcontractA {
    function getMsg() external view returns(string memory);
}

// Base contract implementation 
contract contractA is IcontractA {
    string message;

    // Constructors 
    constructor(string memory _message) {
        message = _message;
    }

    function _getMsg() internal view returns (string memory) {
        return message;
    }

    function getMsg() external override view returns(string memory) {
        return _getMsg();
    }
}

// Sub contract  -  Inheritance base contract 
contract contractB is contractA {
    address admin;

    // Constructors 
    constructor(string memory _message) contractA(_message) {
        admin = msg.sender;
    }

    // Call the base contract function 
    function callA() external view returns(string memory) {
        return _getMsg();
    }
}

If the base contract constructor has no arguments , You also need to provide the base contract constructor in the derived contract , It's just no reference , Fine tune the above code , The base contract constructor has no parameters

32 The adjustment is as follows ：

constructor(string memory _message) contractA() {

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

// Base contract interface 
interface IcontractA {
    function getMsg() external view returns(string memory);
}

// Base contract implementation 
contract contractA is IcontractA {
    string message;

    // Constructors 
    constructor() {
        message = "_message";
    }

    function _getMsg() internal view returns (string memory) {
        return message;
    }

    function getMsg() external override view returns(string memory) {
        return _getMsg();
    }
}

// Sub contract  -  Inheritance base contract 
contract contractB is contractA {
    address admin;

    // Constructors 
    constructor() contractA() {
        admin = msg.sender;
    }

    // Call the base contract function 
    function callA() external view returns(string memory) {
        return _getMsg();
    }
}

contract B Create another contract in A, Call contract A in view Function time , Out of commission view

When a base contract is created in a sub contract , Call your own query function through the newly created base contract （ Use view Modifier ） when , Functions in a sub contract cannot use view Modifier , The contract code is as follows ：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

// Base contract interface 
interface IcontractA {
    function getMsg() external view returns(string memory);
}

// Base contract implementation 
contract contractA is IcontractA {
    string message;

    // Constructors 
    constructor(string memory _message) {
        message = _message;
    }

    function _getMsg() internal view returns (string memory) {
        return message;
    }

    function getMsg() external override view returns (string memory) {
        return _getMsg();
    }
}

// Sub contract  -  Inheritance base contract 
contract contractB is contractA {
    address admin;

    // Constructors 
    constructor(string memory _message) contractA(_message) {
        admin = msg.sender;
    }

    // Call the base contract function 
    function callA() external view returns (string memory) {
        return _getMsg();
    }

    // Create base contract , Call function 
    function callANewContract() external view returns (string memory) {
        contractA contractAddr = new contractA("Hello, I am tracy");
        return contractA(contractAddr).getMsg();
    }
}

The error message is as follows ：

TypeError: Function declared as view, but this expression (potentially) modifies the state and thus requires non-payable (the default) or payable. --> Test/CallContract.sol:43:34: | 43 | contractA contractAddr = new contractA("Hello, I am tracy"); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Remove 42 In a row view Modifier , Deployment contract B, Found calling function callANewContract() It's actually a charge gas Function of fee （ The yellow background is marked as "charge" gas Fee function ）, As shown in the figure below ：