I have contract Users, that contains users list and nftInstance:

contract Users {
    struct UserData{
        User user;
        bool exists;

    mapping (address => UserData) public users;
    NFT public nftInstance;

    constructor() {
        nftInstance = new NFT();

    event UserConnect(User user);

    function connectUser() public  {
        address userAddress = msg.sender;

        if(users[userAddress].exists) emit UserConnect(users[userAddress].user);
        else {
            User user = new User(userAddress, nftInstance);
            users[userAddress].user = user;
            users[userAddress].exists = true;
            emit UserConnect(user);

    function getUser(address _userAddress) public view returns (User){
        return users[_userAddress].user;

And i have User contract. In constructor i get nftInstance to be able to create NFT in User . And store NFTs in one storage. This is my User contract:

contract User {
    address public userAddress;
    NFT private nftInstance;

    constructor (address _userAddress, NFT _nftInstance) {
        userAddress = _userAddress;
        nftInstance = _nftInstance;

    event Collect(string tokenURI);

    function collect() public{
        uint256 tokenId = nftInstance.createNFT(userAddress);
        emit Collect(nftInstance.tokenURI(tokenId));

    function getMyNFTs() public {
        mapping(address => uint256) storage tokenIdsCount = nftInstance.userAddressToTokenId; // 1 VARIANT
        uint256[] memory tokenIds = nftInstance.userAddressToTokenId[userAddress]; // 2 VARIANT

In NFT contract i have such mapping: mapping(address => uint256[]) public userAddressToTokenId; And i try to get this mapping data in User. But this is wrong

1 - TypeError: Type function (address,uint256) view external returns (uint256) is not implicitly convertible to expected type mapping(address => uint256).

2 - ypeError: Indexed expression has to be a type, mapping or array (is function (address,uint256) view external returns (uint256))

So, how to get tokenIds array from mapping of NFT contract instance?

  • I'm amazed that you dared to post this code here ;D
    – Kaneda
    Feb 7, 2022 at 3:03
  • It's okay, just some protest;)
    – Влад
    Feb 7, 2022 at 11:56
  • @Kaneda so, how to interact with mapping from another contract?
    – Влад
    Feb 7, 2022 at 11:58
  • Can you include NFT how tokenIds are defined in the NFT contract? In any case a contract can't access the storage area of another contract directly the only way to do so is for the second contract to have public getter functions.
    – Ismael
    Feb 9, 2022 at 3:25

1 Answer 1


I wrote a getter in the NFT contract to get mapping

function getTokenIdsFromAddress(address _userAddress) public view 
 returns(uint256[] memory) {
    return userAddressToTokenId[_userAddress];

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