ShardedToken

ShardedToken.sol

contract ShardedToken {
    using SafeMath for uint256;

    address owner = msg.sender;
    uint256 private _totalSupply;
    mapping(address => ShardedToken.Extension) private extensions;

    function register() public {
        extensions[msg.sender] = new Token.Extension();
    }
    
    function mint(address to, uint256 amount) public {
        require(msg.sender == owner, "Access denied");
        _totalSupply = _totalSupply.add(amount);
        ShardedToken.Extension(to).receive(address(0), amount);
    }

    library Extension {
        uint256 private _balance;
        mapping(address => uint256) private _allowance;

        function balance() public view returns(uint256) {
            return _balance;
        }

        function transfer(address to, uint256 amount) public {
            _balance = _balance.sub(amount, "Not enough balance");
            ShardedToken.Extension(to).receive(this, amount);
        }

        function receive(address from, uint256 amount) protected {
            _balance = _balance.add(amount);
        }

        //

        function allowance(address to) public view returns(uint256) {
            return _allowance[to];
        }

        function approve(address to, uint256 amount) public {
            require(_allowance[to] == 0 || amount == 0);
            _allowance[to] = amount;
        }

        function transferFrom(address to, uint256 amount) public {
            _allowance[msg.sender] = _allowance[msg.sender].sub(amount);
            transfer(to, amount);
        }
    }
}

This raw concept ended up to this MVP: https://github.com/k06a/ShardedToken