pragma solidity =0.5.16;

contract TestContract {
    bytes feeBytes;
    address feeToSetter;

    mapping(address => mapping(address => address)) public getPair;
    address[] public allPairs;

    constructor(address _feeToSetter) public {
        feeToSetter = _feeToSetter;
    }

    function getF() public returns (address feeToSetter) {}

    function createPair(address tokenA, address tokenB)
        external
        returns (address pair)
    {
        bytes memory bytecode = "01001";
        bytes32 salt = keccak256(abi.encodePacked(tokenA, tokenB));
        assembly {
            pair := create2(0, add(bytecode, 32), mload(bytecode), salt)
        }
    }
}