I'm new to Solidity and coding in general and this code may be a disaster, but I'm learning.

Basically, I'd like to get members of a struct with a function. I can return the entire struct in the form of a tuple in another function (getPairData()), but not when trying to return individual members. When I try accessing the members (getPairMembers()) - I get an error: struct member not found or not visible after argument dependent lookup in struct MapTest.Pair storage... (see photo below)

I think this code may be a little hacky - I wasn't sure how to keep track of multiple datasets from the same user. I tried making a mapping to an array of the structs, but couldn't figure out how to access each one individually so I mapped every address to an integer mapped to the struct array to act as a sort of index(?)

Here's my code:

pragma solidity ^0.8.0;

contract MapTest {

struct Pair {
    uint256 token1;
    uint256 token2;
    uint256 breedStart;
    uint256 breedEnd;

mapping(address => mapping(uint256 => Pair[])) userPairs; 
mapping(address => uint256) pairCount;
mapping(uint256 => bool) isBreeding;

function getRandom() public view returns(uint256){
    uint256 time = block.timestamp;
    uint256 rand = uint256(keccak256(abi.encodePacked(time)));
    return (rand % 360);

function breed(uint256 _token1, uint256 _token2) public {
    require (isBreeding[_token1] == false && isBreeding[_token2] == false);

    uint256 breedTime = getRandom();
    uint256 time = block.timestamp;
    Pair memory pairTest;
    pairTest.breedStart = time;
    pairTest.breedEnd = time + breedTime;
    pairTest.token1 = _token1;
    pairTest.token2 = _token2;
    isBreeding[_token1] = true;
    isBreeding[_token2] = true;
    //function for burning incubator here

function getPairData(address _wallet, uint256 _index) public view returns(Pair[] memory){
    return userPairs[_wallet][_index];

function getPairMembers(address _wallet, uint _index) public view returns(uint256, uint256, uint256, uint256){
    return (userPairs[_wallet][_index].token1, 


The error code I receive is this:

enter image description here

Any help would be greatly appreciated.

1 Answer 1


The logic you used is actually for: mapping(address=>mapping(uint=>Pair)) which is the structure itself instead of the struct array you're defining inside the mapping. To access token1 value, you'll first need to push the items into the Pair[] array like you did here: userPairs[msg.sender][pairCount[msg.sender]].push(pairTest) and then iterate through the mapping array with a for loop.

for(uint i=0;i<userPairs[msg.sender][pairCount[msg.sender]].length;i++)
 return userPairs[msg.sender][pairCount[msg.sender]][i].token1;
  • Thank you so much! That's incredible. So it seems like I might not have even needed to use an array for Pair in the first place when mapping(address=>mapping(uint=>Pair)) and accessing by index seems to work fine. Would you recommend against this, or would that implementation be fine as well? Again, thanks so much for your help. You're a lifesaver.
    – Ethan Z.
    Oct 5, 2021 at 20:35
  • No worries, glad I could help! I'm still learning to work with mappings and arrays atm, but the way I would do it would be to declare 2 more values in the Pair struct: an uint id to keep count of the pair and an address breeder to keep track of the user that is initiating the breed process. After that I would change the mapping mapping(address=>mapping(uint=>Pair)) into this: mapping(address => Pair[]) because I suppose you want to keep track of the number of pairs each address generates.
    – Icarus23
    Oct 5, 2021 at 21:48

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