Getting address from struct mapping

Question

I have a struct in a library:

// lib
struct Data {
    int256 count;
    mapping(address => int256) indices;
    mapping(int256 => address) items;
}

// Also append function in lib
function append(Data storage self, address addr)
internal
returns (bool) {
    if (addr == ZERO_ADDRESS) {
        return false;
    }

    int256 index = self.indices[addr] - 1;
    if (index >= 0 && index < self.count) {
        return false;
    }

    self.count++;
    self.indices[addr] = self.count;
    self.items[self.count] = addr;
    return true;
}

And then another contract that uses this library struct:

// Contract.sol
using LibMap for LibMap.Data;
mapping(address => LibMap.Data) public addresses;

And then in a function I push to it

addresses[msg.sender].append(addr);

From the front end with web3 I can do contract.addresses(msg.sender) where msg.sender is the address from earlier in the contract that was set and it will return a length/count of how many have been appended. But how would I rather read all the addresses that have been pushed instead of a length/count?

Would I need a function in the contract for this?

Answer 1

If you want to read all the addresses appended to any given Data, you will have to do it iteratively.

You could do this on the frontend, by querying the contract for what the value of addresses[msg.sender].count, and then loop through and get the value of everything in addresses[msg.sender].items one at a time (from 1 to count).

The alternative would just be to do the same sort of thing with a function in your contract, loop through and return an array of them.

You can't just return a mapping though.