Contract which describes InheritedStorage approach for proxies and diamonds.

InheritedStorage.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.0;

contract Storage {
  uint firstVar;
  uint secondVar;
  string thirdVar;
  string fourthVar;
}

contract FacetA is Storage {

  function getVars() public view returns(uint, uint) {
    return (firstVar, secondVar);
  }
  
}

contract FacetB is Storage {

  function getVars() public returns(string memory, string memory) {
    thirdVar = "Ashwin";
    fourthVar = "Yardi";
    return (thirdVar, fourthVar);
  }
  
}