I have a factory contract with the below code:

//SPDX-License-Identifier: no-license
pragma solidity ^0.8.9;

interface ChildInterface {
    function getStateVariable() external returns(uint);

contract Child is ChildInterface{
    uint public x;
    address public owner;

    constructor(address _owner, uint _x) {
        x = _x;
        owner = _owner;

    function getStateVariable() public view returns(uint){
        return x;

contract Parent {

 Child[] public childContracts;

 function createContract(uint seller) public {
        // - create a new Lottery instance with msg.sender as seller.
        Child newContract = new Child(msg.sender, seller);

        // - push the newly created contract to lotteries array.

function getValidChildContractAddresses() public returns(bytes memory addresses){
     Child[] memory validChildContracts;
     for(uint i = 0;i <= childContracts.length;i++){
         if(ChildInterface(childContracts[i]).getStateVariable() == 10){
              validChildContracts[i] = address(childContracts[i]);

     addresses = abi.encode(validChildContracts);

I am trying to get all the addreses of the child contracts are stored in the childContracts that matches a condition and convert them as bytes to be returned in the getCreatedContractAddresses() function.

I'm getting the error: 'TypeError: Type address is not implicitly convertible to expected type contract Child.' in this line: validChildContracts[i] = address(childContracts[i]);.

May I know how to achieve that?

  • Your code looks fine. Are you facing any errors? If so, can you post them?
    – pbsh
    Commented Jan 19, 2022 at 8:48
  • Hi, I updated the code with error and a full code to be run on remix.
    – toddash
    Commented Jan 19, 2022 at 13:56

1 Answer 1


The issue is in the following line

Child[] memory validChildContracts;

This created the variable validChildContracts of type Child[]. However, it needs to be of type address[] as we aren't creating an instance of the child, but merely storing its' address.

address[] memory validChildContracts; should fix the error.

  • Hi, I actually need to have the Child[] in validChildContracts so that I can use it to change state varialbe by calling methods with in the child contract like: ChildInterface(validChildContracts[i]).childContractMethod(). Is it possible even If I use it as address[] memory validChildContracts?
    – toddash
    Commented Jan 19, 2022 at 15:23
  • I am trying to use this functionality with chainlink's checkupkeep and performupkeep functions. like passing the validChildContracts list of addreses to the performupkeep function and call ChildInterface(validChildContracts[i]).somefunctionInChildContract(). May I know if that will make changes to the state variables deployed contract under the validChildContracts[i] address (where i is a local variable in for loop)?
    – toddash
    Commented Jan 19, 2022 at 15:28
  • 1
    What you explained in ChildInterface(validChildContracts[i]).childContractMethod() is right. Its creating an instance of ChildItnterface at the address validChildContracts[i]. You can then interact with it normally.
    – pbsh
    Commented Jan 19, 2022 at 16:01
  • hi @pbsh, I am getting the following error when I try running getValidChildContractAddresses() in Parent contract: Note: The called function should be payable if you send value and the value you send should be less than your current balance.
    – toddash
    Commented Jan 20, 2022 at 3:53
  • Are you sure it's coming from getValidChildContractAddresses because there isn't any code inside it that's sending ether?
    – pbsh
    Commented Jan 20, 2022 at 5:17

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