custom-transfer-restrictions-erc20.sol

pragma solidity ^0.4.24;
//interface for parent contract of any child token

/*
- Parent contract interface for adding custom logic before calling the 'transfer' function 
in the ERC721/ERC20 child chain contract on the Matic chain
- 'transfer' executes the 'beforeTransfer' of this interface contract
- It must follow this interface and return a bool value and 
- in case of ERC20 contracts, it should not have 'require' statements and instead return 'false'
- IParentToken contract address in childchain contract can be updated by owner set in rootchain contract only
while mapping new token in rootchain

*/

interface IParentToken {
  function beforeTransfer(address sender, address to, uint256 value) public returns(bool);
}

//
// sample 'parentContract' implementation can contain any logic, but it must implement the 'beforeTransfer' function
//

pragma solidity ^0.4.24;

import "openzeppelin-solidity/contracts/ownership/Ownable.sol";

import "./IParentToken.sol";
// demo token parent contract  

contract ParentTokenMock is IParentToken, Ownable {
  mapping (address => bool) isAllowed;
  function beforeTransfer(address sender, address to, uint256 value) public returns(bool) {
    return isAllowed[sender];
  }

  function updatePermission(address user) public onlyOwner {
    require(user != address(0x0));
    isAllowed[user] = !isAllowed[user];
  }
}