Gist for the new post in medium : Interacting with other contracts from within a contract

Token.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.4.22 <0.8.0;


contract OwnedToken {
    TokenCreator creator;
    address owner;
    bytes32 public name;
    constructor(bytes32 _name) {
        owner = msg.sender;
        creator = TokenCreator(msg.sender);
        name = _name;
    }

    function changeName(bytes32 newName) public {
        if (msg.sender == address(creator))
            name = newName;
    }

    function transfer(address newOwner) public {
        if (msg.sender != owner) return;

        if (creator.isTokenTransferOK(owner, newOwner))
            owner = newOwner;
    }
}


contract TokenCreator {
    event TokenCreated(bytes32 name, address tokenAddress);

    function createToken(bytes32 name)
        public
        returns (OwnedToken tokenAddress)
    {
        tokenAddress =  new OwnedToken(name);
        emit TokenCreated(name, address(tokenAddress));
    }

    function changeName(OwnedToken tokenAddress, bytes32 name) public {

        tokenAddress.changeName(name);
    }

    function isTokenTransferOK(address currentOwner, address newOwner)
        public
        pure
        returns (bool ok)
    {

        return keccak256(abi.encodePacked(currentOwner, newOwner))[0] == 0x7f;
    }
}