Dummy.sol

contract Dummy {
    address impl;

    constructor (address _impl) public {
      impl = _impl;
    }

    function () public {
     require(msg.sig != 0x0);
     address _impl = impl;
     assembly {
        let ptr := mload(0x40)
        calldatacopy(ptr, 0, calldatasize)
        let result := delegatecall(gas, _impl, ptr, calldatasize, ptr, 0)
        let size := returndatasize
        returndatacopy(ptr, 0, size)
        switch result
        case 0 { revert(ptr, size) }
        default { return(ptr, size) }
    }
  }
  
  //This function can make the current instance upgradeable, instead of only newly spawned instances
  // Acces control not included for simplicity (you could use Ownable.sol from OpenZeppelin)
  function changeImplementation(address _impl) public {
    impl = _impl;
  }
}