example.sol

pragma solidity ^0.8.0;
/**
 * @title ERC721Registry
 * @notice A registry contract for tracking ERC721 contracts.
 *         Allows adding ERC721 contract addresses up to a configurable limit.
 * @dev EIP-8042 Diamond Storage is used to organize and manage access to storage.
 */
contract ERC721Registry {

  /// @notice Reverts when the registry reaches its configured capacity.
  error ERC721RegistryFull();
  
  bytes32 constant STORAGE_POSITION = keccak256("myproject.erc721.registry");
  
  struct ERC721RegistryStorage {
    address[] erc721Contracts;
    uint256 registryLimit;    
  }

  function getStorage() internal pure  returns (ERC721RegistryStorage storage s) {
    bytes32 position = STORAGE_POSITION;
    assembly {
      s.slot := position
    }
  }

  function setRegistryLimit(uint256 _newLimit) internal {
    getStorage().registryLimit = _newLimit;
  }

  function addERC721Contract(address _erc721Contract) internal { 
    ERC721RegistryStorage storage s = getStorage();
    if(s.erc721Contracts.length == s.registryLimit) {
      revert ERC721RegistryFull();
    }    
    s.erc721Contracts.push(_erc721Contract);        
  }

  /// @notice Returns a list of all registered ERC721 contract addresses.
  /// @return Array of registered ERC721 contract addresses.
  function getERC721Registry() internal view returns (address[] memory) {
    return getStorage().erc721Contracts;
  }
}