This is the mapping containing the struct.

    mapping(address => UserFessInfo) public userFeesInfo;

This is the struct UserFeeInfo

    struct UserFessInfo {
    uint256 stakedAmount;
    uint256 stakedWeight;
    uint256 lastStakedBlock;
    uint256 lastClaimedBlock;
    mapping(uint256 => uint256) epochToUserStakedWeight;

Now, to retrieve these values for testing I tried to use this syntax in foundry test file.

        uint256 stakedAmount,
        uint256 stakedWeight,
        uint256 lastStakedBlock,
        uint256 lastClaimedBlock,
        mapping(uint256 => uint256) epochToUserStakedWeight
    ) = core.userFeesInfo(bob);

But later I realized that it contains mapping and needed the data location to be set as storage. And I was right as I got this error.

error[6651]: test/StakeAndClaim.t.sol:85:13: TypeError: Data location must be "storage" for variable, but none was given.
        mapping(uint256 => uint256) epochToUserStakedWeight

I am confused about how to do this. How to store the struct that is returned from the mapping?

1 Answer 1


I believe you need to add 'storage' (or 'memory') in the following line:

mapping(uint256 => uint256) storage epochToUserStakedWeight
  • Tried this, but it seems like we are getting the mapping. When I added storage, I got another error saying that LHS has 5 arguments and RHS has 4 arguments. What are your views on this? Like, calling a public mapping doesn't return the mapping inside the struct??? Jul 3, 2023 at 10:22
  • Could it be because you have called it on a mapping or another object? solidity core.userFeesInfo(bob); Is 'core' an object of some type? If it is, the method is called on this object, and that would fill one of the 5 arguments you have set. Jul 3, 2023 at 18:02
  • Core is a deployed instance of contract. I have deployed it using the new keyword, as we do in Foundry. Jul 4, 2023 at 3:34

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