如何将结构映射到数组？

Question

我有一个名为Meeting的结构，它包含一系列地址。我想在地址回复到会议之前检查地址是否不存在，所以我创建了一个名为hasRSVPed的映射。(我可以循环遍历地址数组，但效率很低)。

我试图将创建的会议推入一系列会议，但是如果会议包含映射，我该如何做呢？

当我尝试这样做时，我得到了下面的错误

TypeError: Uninitialized mapping. Mappings cannot be created dynamically, you have to assign them from a state variable.

 struct Meeting {
        address meeting_creator;
        uint256 meetingID;
        string name;
        string description;
        uint256 start_date;
        uint256 end_date;
        uint256 max_tickets;
        uint256 ticket_price;
        uint256 current_tickets_sold;
        address[] attendees;
        mapping(address => bool) hasRSVPed;

    }

Meeting[] public meetingArray;

function create_meeting(string memory _name, string memory _description, uint _startTime, uint _endTime, uint _maxTickets,
    uint256 _ticketPrice) public returns (uint256 meetingID) {

        address[] memory adr;
        mapping(address => bool) memory RSVPed;

        totalMeetings += 1;
        meetingID = totalMeetings;

        meetingArray.push(Meeting(msg.sender, meetingID, _name, _description, _startTime, _endTime, _maxTickets, _ticketPrice, 0, adr, RSVPed));

        Meeting storage m = meetings[totalMeetings];
        m.meeting_creator = msg.sender;
        m.meetingID = meetingID;
        m.name = _name;
        m.description = _description;
        m.start_date = _startTime;
        m.end_date = _endTime;
        m.max_tickets = _maxTickets;
        m.ticket_price = _ticketPrice;
        m.current_tickets_sold = 0;
        m.attendees = adr;
        m.hasRSVPed = RSVPed;
}

Answer 1

您正在尝试将动态映射推送到数组。据我所知，这可能是不可能的，因为数组本身在本质上是动态的。因此，如果一开始无法确定映射的大小，那么solidity就无法正确计算EVM中的存储槽。或者，这可能会导致汽油成本过高。

因此，我建议使用映射(uint => bool) hasRSVPed来跟踪具有唯一id的会议是否为RSVPed。

我有一个代码片段，用于实现我指出的代码。

pragma solidity ^0.8.0;
contract meeting {
    uint totalMeetings;
    struct Meeting {
        address meeting_creator;
    }
    mapping(uint => bool) hasRSVPed;
    mapping(uint => Meeting) meetings;

Meeting[] private meetingArray;

function create_meeting(string memory _name, string memory _description, uint _startTime, uint _endTime, uint _maxTickets,
    uint256 _ticketPrice) public returns (uint256 meetingID) {

        address[] memory adr;
        totalMeetings += 1;
        Meeting storage m = meetings[totalMeetings];
        m.meeting_creator = msg.sender;
        hasRSVPed[totalMeetings] = true;
}