Tutorial on inheritance

inheritance.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.17;

contract Parent {
    function foo() public pure virtual returns (string memory) {
        return "A";
    }

    function bar() public pure virtual returns (string memory) {
        return "B";
    }

    function available() public pure returns (string memory) {
        return "Yes";
    }
}

contract Child is Parent {
    function foo() public pure override returns (string memory) {
        return "B";
    }

    function bar() public pure virtual override returns (string memory) {
        return "A";
    }
}

contract GrandChild is Child {
    function bar () public pure override returns (string memory) {
        return "Grand child";
    }
}