For/If Loop has no errors but does not push the value to the array

Question

I am trying to create a whitelist. I've used a for and if loop to check if the msg.sender already exists in the array. When the whitelist() function is run, no errors are returned, but when I run check(), it tells me the address doesn't exist in the array, same thing with directing fetching the array.

//SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract SelfWhitelist {

    address[] public addressWhitelist;

    function whitelist() public returns(string memory) {
        for(uint i = 0; i < addressWhitelist.length; i++) {
            if(addressWhitelist[i] != msg.sender) {
                addressWhitelist.push(msg.sender);
                return "Whitelisted!";
            }
        }
        return "Already whitelisted!";
    }

    function check() public view returns (bool){
        for(uint i = 0; i < addressWhitelist.length; i++){
            if(addressWhitelist[i] == msg.sender)
                return true;
        }
        return false;
    }

}

I added this block of code to check for duplicate entries in the array.

for(uint i = 0; i < addressWhitelist.length; i++) {
            if(addressWhitelist[i] != msg.sender) {
                addressWhitelist.push(msg.sender);
                return "Whitelisted!";
            }

Expected for no errors and my address being pushed to the array.

The code ran without errors, but nothing was added to the array.

Answer 1

I would use mapping type to hold the whitelisted addresses, then you don't have to loop over the array

contract SelfWhitelist {

    mapping(address => bool) public addressWhitelist;

    function whitelist() public returns(string memory) {
        if (check()) {
            return "Already whitelisted!";
        }
        addressWhitelist[msg.sender] = true;
        return "Whitelisted!";
    }

    function check() public view returns (bool) {

        return addressWhitelist[msg.sender];
    }
}

---

And in your code, seems you have logical issues:

 for(uint i = 0; i < addressWhitelist.length; i++) {
    if(addressWhitelist[i] != msg.sender) {
        addressWhitelist.push(msg.sender);
        return "Whitelisted!";
    }
}

• if the array is empty, the loop never executes, so nothing will be added
• if the first item is not msg.sender, msg.sender will be whitelisted, even though it might be already whitelisted.