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I was reading a tutorial on a medium about how to return an array of structs. This is the code they have for doing it. 

pragma solidity ^0.4.13;

contract Project
{
    struct Person {
        address addr;
        uint funds;
    }

    Person[] people;

    function getPeople(uint[] indexes)
        public
        returns (address[], uint[])
    {
        address[] memory addrs = new address[](indexes.length);
        uint[]    memory funds = new uint[](indexes.length);

        for (uint i = 0; i < indexes.length; i++) {
            Person storage person = people[indexes[i]];
            addrs[i] = person.addr;
            funds[i] = person.funds;
        }

        return (addrs, funds);
    }
}

The uint[] index argument however makes no sense to me. Can someone please explain what it is and what it does?

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  • Do you mean the uint[] indexes argument? – valkn0t Jul 17 '18 at 13:54
  • Yep, that's what I meant. @valkn0t – user3078335 Jul 17 '18 at 13:55
0

uint[] indexes is used to access the data of people located at the indices passed to the function, to build an array of structs to return.

For example: if there were 100 Person stored in the contract, and we wanted an array of just the Person's stored at [1, 2, 3], we pass that array as uint[] indexes and receive the addresses and funds located at people[1], people[2], and people[3].

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  • Thanks for your answer. It makes sense. What it if I wanted to return every person in people. [1... people.length] ? Still a newbie to solidity :) – user3078335 Jul 17 '18 at 14:05
  • If you wanted to return the entire array you could simply remove/ignore the argument uint[] indexes and loop over people[] til people.length, putting the addresses and funds into the correct arrays, and returning them like how it's implemented in the code above. Also just to be clear: solidity is simply a Javascript-esque language used to write and compile smart contracts; these questions are more Javascript questions than Solidity. If you have further questions about things like loops and arrays and such, I'd suggest researching Javascript code before Solidity. – valkn0t Jul 17 '18 at 14:11
  • ah! gotcha! I will try that approach. Thank you very much for your help!! – user3078335 Jul 17 '18 at 14:13
  • I will do that. Very new to javascript as well. Thanks for your help. – user3078335 Jul 17 '18 at 14:14

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