Using immutable keyword

SimpleDonationManager.sol

pragma solidity >=0.6.5;
contract SimpleDonationManager {
    uint256 immutable minDonation = 42;
    uint256 immutable maxDonation = calcMaxDonation();
    address immutable owner;
    constructor() public {
        owner = msg.sender;
        // Error: Immutables cannot be read in constructor.
        // assert(minDonation <= maxDonation);
        // Error: Immutables can only be assigned once.
        // owner = address(0);
    }
    function withdraw(uint256 amount) public {
        require(msg.sender == owner); // Requires no sload!
        msg.sender.transfer(amount);
    }
    receive() external payable {
        require(msg.value >= minDonation && msg.value <= maxDonation);
    }
    function calcMaxDonation() internal pure returns (uint256 max) {
        max = 10000 * 42;
        // Error: Cannot read from Immutables in construction context.
        // max = 10000 * minDonation;
    }
    // Error: cannot write to Immutables from runtime context.
    // function changeOwner(address newOwner) external {
    //     owner = newOwner;
    // }
}