Solidity Error; TypeError: Struct containing a (nested) mapping cannot be constructed

Question

I tried modify the castVote function to allow voters to change their vote on a particular proposal.I also tried to figure out a new way to track which addresses have already voted on which proposal. But i keep running this this error :

TypeError: Struct containing a (nested) mapping cannot be constructed.
  --> src/Voting.sol:19:47:
   |
19 |         Proposal memory newProposalInstance = Proposal({
   |                                               ^ (Relevant source part starts here and spans across multiple lines).

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract Voting {
    struct Proposal {
        address target;
        bytes data;
        uint yesCount;
        uint noCount;
        mapping(address => bool) hasVoted; // Keep track of whether an address has voted
    }

    Proposal[] public proposals;

    function newProposal(address _target, bytes calldata _data) external {
        Proposal memory newProposalInstance = Proposal({
            target: _target,
            data: _data,
            yesCount: 0,
            noCount: 0
        });

        proposals.push(newProposalInstance);
    }

    function castVote(uint proposalId, bool supportsProposal) external {
        require(proposalId < proposals.length, "Invalid proposalId");

        Proposal storage proposal = proposals[proposalId];

        // Check if the voter has already voted
        require(!proposal.hasVoted[msg.sender], "Address has already voted");

        // If the voter previously voted yes, decrement yesCount; if voted no, decrement noCount
        if (proposal.hasVoted[msg.sender]) {
            if (proposal.hasVoted[msg.sender] == true) {
                proposal.yesCount--;
            } else {
                proposal.noCount--;
            }
        }

        // Update the vote and mark the voter as having voted
        if (supportsProposal) {
            proposal.yesCount++;
        } else {
            proposal.noCount++;
        }
        proposal.hasVoted[msg.sender] = supportsProposal;
    }
}

Please help figure out how to solve the error shared above.

Answer 1

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract Voting {
    struct Proposal {
        address target;
        bytes data;
        uint yesCount;
        uint noCount;
        mapping(address => bool) hasVoted; // Keep track of whether an address has voted
    }

    Proposal[] public proposals;

    function newProposal(address _target, bytes calldata _data) external {
        Proposal storage newProposalInstance = proposals.push();

        newProposalInstance.target = _target;
        newProposalInstance.data = _data;
        newProposalInstance.yesCount = 0;
        newProposalInstance.noCount = 0;
    }

    function castVote(uint proposalId, bool supportsProposal) external {
        require(proposalId < proposals.length, "Invalid proposalId");

        Proposal storage proposal = proposals[proposalId];

        // Check if the voter has already voted
        require(!proposal.hasVoted[msg.sender], "Address has already voted");

        // If the voter previously voted yes, decrement yesCount; if voted no, decrement noCount
        if (proposal.hasVoted[msg.sender]) {
            if (proposal.hasVoted[msg.sender] == true) {
                proposal.yesCount--;
            } else {
                proposal.noCount--;
            }
        }

        // Update the vote and mark the voter as having voted
        if (supportsProposal) {
            proposal.yesCount++;
        } else {
            proposal.noCount++;
        }
        proposal.hasVoted[msg.sender] = supportsProposal;
    }
}

Tweaking the syntax and the instantiation order slightly should fix that error in your case.