use upgradable storage

src/transfer-validated/ERC1155ShipyardTransferValidated.sol

@@ -4,11 +4,13 @@ pragma solidity ^0.8.17;
 import {Ownable} from "solady/src/auth/Ownable.sol";
 import {ERC1155} from "solady/src/tokens/ERC1155.sol";
 import {ERC1155ConduitPreapproved_Solady} from "../tokens/erc1155/ERC1155ConduitPreapproved_Solady.sol";
-import {TokenTransferValidator} from "./lib/TokenTransferValidator.sol";
+import {TokenTransferValidator, TokenTransferValidatorStorage} from "./lib/TokenTransferValidator.sol";
 import {ICreatorToken} from "../interfaces/transfer-validated/ICreatorToken.sol";
 import {ITransferValidator1155} from "../interfaces/transfer-validated/ITransferValidator.sol";
 
 contract ERC1155ShipyardTransferValidated is ERC1155ConduitPreapproved_Solady, TokenTransferValidator, Ownable {
+    using TokenTransferValidatorStorage for TokenTransferValidatorStorage.Layout;
+
     constructor(address initialTransferValidator) ERC1155ConduitPreapproved_Solady() {
         // Set the initial contract owner.
         _initializeOwner(msg.sender);
@@ -46,7 +48,7 @@ contract ERC1155ShipyardTransferValidated is ERC1155ConduitPreapproved_Solady, T
     ) internal virtual override {
         if (from != address(0) && to != address(0)) {
             // Call the transfer validator if one is set.
-            address transferValidator = _transferValidator;
+            address transferValidator = TokenTransferValidatorStorage.layout()._transferValidator;
             if (transferValidator != address(0)) {
                 for (uint256 i = 0; i < ids.length; i++) {
                     ITransferValidator1155(transferValidator).validateTransfer(msg.sender, from, to, ids[i], amounts[i]);

src/transfer-validated/ERC721ShipyardTransferValidated.sol

@@ -4,11 +4,13 @@ pragma solidity ^0.8.17;
 import {Ownable} from "solady/src/auth/Ownable.sol";
 import {ERC721} from "solady/src/tokens/ERC721.sol";
 import {ERC721ConduitPreapproved_Solady} from "../tokens/erc721/ERC721ConduitPreapproved_Solady.sol";
-import {TokenTransferValidator} from "./lib/TokenTransferValidator.sol";
+import {TokenTransferValidator, TokenTransferValidatorStorage} from "./lib/TokenTransferValidator.sol";
 import {ICreatorToken} from "../interfaces/transfer-validated/ICreatorToken.sol";
 import {ITransferValidator721} from "../interfaces/transfer-validated/ITransferValidator.sol";
 
 contract ERC721ShipyardTransferValidated is ERC721ConduitPreapproved_Solady, TokenTransferValidator, Ownable {
+    using TokenTransferValidatorStorage for TokenTransferValidatorStorage.Layout;
+
     constructor(address initialTransferValidator) ERC721ConduitPreapproved_Solady() {
         // Set the initial contract owner.
         _initializeOwner(msg.sender);
@@ -35,7 +37,7 @@ contract ERC721ShipyardTransferValidated is ERC721ConduitPreapproved_Solady, Tok
     function _beforeTokenTransfer(address from, address to, uint256 id) internal virtual override {
         if (from != address(0) && to != address(0)) {
             // Call the transfer validator if one is set.
-            address transferValidator = _transferValidator;
+            address transferValidator = TokenTransferValidatorStorage.layout()._transferValidator;
             if (transferValidator != address(0)) {
                 ITransferValidator721(transferValidator).validateTransfer(msg.sender, from, to, id);
             }

src/transfer-validated/lib/TokenTransferValidator.sol

@@ -3,31 +3,46 @@ pragma solidity ^0.8.17;
 
 import {ICreatorToken} from "../../interfaces/transfer-validated/ICreatorToken.sol";
 
+library TokenTransferValidatorStorage {
+    struct Layout {
+        /// @dev Store the transfer validator. The null address means no transfer validator is set.
+        address _transferValidator;
+    }
+
+    bytes32 internal constant STORAGE_SLOT = keccak256("contracts.storage.tokenTransferValidator");
+
+    function layout() internal pure returns (Layout storage l) {
+        bytes32 slot = STORAGE_SLOT;
+        assembly {
+            l.slot := slot
+        }
+    }
+}
+
 /**
  * @title  TokenTransferValidator
  * @notice Functionality to use a transfer validator.
  */
 abstract contract TokenTransferValidator is ICreatorToken {
-    /// @dev Store the transfer validator. The null address means no transfer validator is set.
-    address internal _transferValidator;
+    using TokenTransferValidatorStorage for TokenTransferValidatorStorage.Layout;
 
     /// @notice Revert with an error if the transfer validator is being set to the same address.
     error SameTransferValidator();
 
     /// @notice Returns the currently active transfer validator.
     ///         The null address means no transfer validator is set.
     function getTransferValidator() external view returns (address) {
-        return _transferValidator;
+        return TokenTransferValidatorStorage.layout()._transferValidator;
     }
 
     /// @notice Set the transfer validator.
     ///         The external method that uses this must include access control.
     function _setTransferValidator(address newValidator) internal {
-        address oldValidator = _transferValidator;
+        address oldValidator = TokenTransferValidatorStorage.layout()._transferValidator;
         if (oldValidator == newValidator) {
             revert SameTransferValidator();
         }
-        _transferValidator = newValidator;
+        TokenTransferValidatorStorage.layout()._transferValidator = newValidator;
         emit TransferValidatorUpdated(oldValidator, newValidator);
     }
 }