No matching declaration found error in Solidity

Question

The code I have:

function approveRequest(uint256 index) public {
    Request storage request = requests[index];

    require(approvers[msg.sender]);
    require(!requests[index].approvals[msg.sender]);

    requests[index].approvals[msg.sender] = true;
    requests[index].approvalCount++;

    // ...
}

is giving the following error:

No matching declaration found after argument-dependent lookup.

at the require

Answer 1

You are using an array which means your approvers stored like index - address. With address type you can check if the specified index contains needed address. For example:

require(approvers[0] == address(0xa846bc19E8ab8Bb0e0bf386853D8C5e199F0Af9b)

To check if there is a needed address in the whole array, you need to write a loop which is very gas-expensive. To save gas and time, you can use an mapping. It assumes that all possible values are exist and always returns false or 0 if some value was not specified directly. You can use is like this:

mapping (address => bool) approvers