LoveLetter-views.sol

contract LoveLetter {
    ...

    function readMessage(uint256 id)
        external
        view
        returns (string memory message)
    {
        message = letters[id].message;
    }

    function checkOpened(uint256 id) external view returns (bool opened) {
        opened = letters[id].opened;
    }

    function getEtherAmount(uint256 id)
        external
        view
        returns (uint256 etherAmount)
    {
        etherAmount = letters[id].etherAmount;
    }

    function getSender(uint256 id) external view returns (address sender) {
        sender = senders[id];
    }

    function getReceiver(uint256 id) external view returns (address receiver) {
        receiver = receivers[id];
    }
}