use immutable value to save gas

contracts/gateway/L1BaseGateway.sol

@@ -1,33 +1,27 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
 pragma solidity ^0.8.0;
 
-import {UUPSUpgradeable} from "@openzeppelin/contracts-upgradeable/proxy/utils/UUPSUpgradeable.sol";
 import {IArbitrator} from "../interfaces/IArbitrator.sol";
 import {IL1Gateway} from "../interfaces/IL1Gateway.sol";
 
-abstract contract L1BaseGateway is IL1Gateway, UUPSUpgradeable {
+abstract contract L1BaseGateway is IL1Gateway {
     /// @notice The arbitrator to confirm synchronization
-    IArbitrator public arbitrator;
+    IArbitrator public immutable arbitrator;
 
     /**
      * @dev This empty reserved space is put in place to allow future versions to add new
      * variables without shifting down storage in the inheritance chain.
      * See https://docs.openzeppelin.com/contracts/4.x/upgradeable#storage_gaps
      */
-    uint256[49] private __gap;
+    uint256[50] private __gap;
 
     /// @dev Modifier to make sure the caller is the known arbitrator.
     modifier onlyArbitrator() {
         require(msg.sender == address(arbitrator), "Not arbitrator");
         _;
     }
 
-    function __L1BaseGateway_init(IArbitrator _arbitrator) internal onlyInitializing {
-        __UUPSUpgradeable_init();
-        __L1BaseGateway_init_unchained(_arbitrator);
-    }
-
-    function __L1BaseGateway_init_unchained(IArbitrator _arbitrator) internal onlyInitializing {
+    constructor(IArbitrator _arbitrator) {
         arbitrator = _arbitrator;
     }
 }

contracts/gateway/L2BaseGateway.sol

@@ -1,32 +1,26 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
 pragma solidity ^0.8.0;
 
-import {UUPSUpgradeable} from "@openzeppelin/contracts-upgradeable/proxy/utils/UUPSUpgradeable.sol";
 import {IL2Gateway} from "../interfaces/IL2Gateway.sol";
 
-abstract contract L2BaseGateway is IL2Gateway, UUPSUpgradeable {
+abstract contract L2BaseGateway is IL2Gateway {
     /// @notice The zkLink contract
-    address public zkLink;
+    address public immutable zkLink;
 
     /**
      * @dev This empty reserved space is put in place to allow future versions to add new
      * variables without shifting down storage in the inheritance chain.
      * See https://docs.openzeppelin.com/contracts/4.x/upgradeable#storage_gaps
      */
-    uint256[49] private __gap;
+    uint256[50] private __gap;
 
     /// @dev Ensure withdraw come from zkLink
     modifier onlyZkLink() {
         require(msg.sender == zkLink, "Not zkLink contract");
         _;
     }
 
-    function __L2BaseGateway_init(address _zkLink) internal onlyInitializing {
-        __UUPSUpgradeable_init();
-        __L2BaseGateway_init_unchained(_zkLink);
-    }
-
-    function __L2BaseGateway_init_unchained(address _zkLink) internal onlyInitializing {
+    constructor(address _zkLink) {
         zkLink = _zkLink;
     }
 }

contracts/gateway/arbitrum/ArbitrumL1Gateway.sol

@@ -10,7 +10,7 @@ import {IArbitrumGateway} from "../../interfaces/arbitrum/IArbitrumGateway.sol";
 
 contract ArbitrumL1Gateway is IArbitrumGateway, L1BaseGateway, BaseGateway {
     /// @notice Arbitrum inbox on local chain
-    Inbox public inbox;
+    Inbox public immutable inbox;
 
     /// @dev Modifier to make sure the original sender is gateway on remote chain.
     modifier onlyRemoteGateway() {
@@ -22,13 +22,14 @@ contract ArbitrumL1Gateway is IArbitrumGateway, L1BaseGateway, BaseGateway {
         _;
     }
 
-    function initialize(IArbitrator _arbitrator, Inbox _inbox) external initializer {
-        __L1BaseGateway_init(_arbitrator);
-        __BaseGateway_init();
-
+    constructor(IArbitrator _arbitrator, Inbox _inbox) L1BaseGateway(_arbitrator) {
         inbox = _inbox;
     }
 
+    function initialize() external initializer {
+        __BaseGateway_init();
+    }
+
     function sendMessage(
         uint256 _value,
         bytes memory _callData,

contracts/gateway/arbitrum/ArbitrumL2Gateway.sol

@@ -17,8 +17,9 @@ contract ArbitrumL2Gateway is IArbitrumGateway, L2BaseGateway, BaseGateway {
         _;
     }
 
-    function initialize(address _zkLink) external initializer {
-        __L2BaseGateway_init(_zkLink);
+    constructor(address _zkLink) L2BaseGateway(_zkLink) {}
+
+    function initialize() external initializer {
         __BaseGateway_init();
     }
 

contracts/gateway/ethereum/EthereumGateway.sol

@@ -2,17 +2,24 @@
 pragma solidity ^0.8.0;
 
 import {OwnableUpgradeable} from "@openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol";
+import {UUPSUpgradeable} from "@openzeppelin/contracts-upgradeable/proxy/utils/UUPSUpgradeable.sol";
 import {ReentrancyGuardUpgradeable} from "@openzeppelin/contracts-upgradeable/security/ReentrancyGuardUpgradeable.sol";
 import {IArbitrator} from "../../interfaces/IArbitrator.sol";
 import {L2BaseGateway} from "../L2BaseGateway.sol";
 import {L1BaseGateway} from "../L1BaseGateway.sol";
 
-contract EthereumGateway is L1BaseGateway, L2BaseGateway, OwnableUpgradeable, ReentrancyGuardUpgradeable {
-    function initialize(IArbitrator _arbitrator, address _zkLink) external initializer {
-        __L1BaseGateway_init(_arbitrator);
-        __L2BaseGateway_init(_zkLink);
+contract EthereumGateway is
+    L1BaseGateway,
+    L2BaseGateway,
+    OwnableUpgradeable,
+    UUPSUpgradeable,
+    ReentrancyGuardUpgradeable
+{
+    constructor(IArbitrator _arbitrator, address _zkLink) L1BaseGateway(_arbitrator) L2BaseGateway(_zkLink) {}
 
+    function initialize() external initializer {
         __Ownable_init();
+        __UUPSUpgradeable_init();
         __ReentrancyGuard_init();
     }
 

contracts/gateway/linea/LineaGateway.sol

@@ -7,14 +7,14 @@ import {ILineaGateway} from "../../interfaces/linea/ILineaGateway.sol";
 
 abstract contract LineaGateway is BaseGateway, ILineaGateway {
     /// @notice Linea message service on local chain
-    IMessageService public messageService;
+    IMessageService public immutable messageService;
 
     /**
      * @dev This empty reserved space is put in place to allow future versions to add new
      * variables without shifting down storage in the inheritance chain.
      * See https://docs.openzeppelin.com/contracts/4.x/upgradeable#storage_gaps
      */
-    uint256[49] private __gap;
+    uint256[50] private __gap;
 
     /// @dev Modifier to make sure the caller is the known message service.
     modifier onlyMessageService() {
@@ -28,13 +28,12 @@ abstract contract LineaGateway is BaseGateway, ILineaGateway {
         _;
     }
 
-    function __LineaGateway_init(IMessageService _messageService) internal onlyInitializing {
-        __BaseGateway_init();
-        __LineaGateway_init_unchained(_messageService);
+    constructor(IMessageService _messageService) {
+        messageService = _messageService;
     }
 
-    function __LineaGateway_init_unchained(IMessageService _messageService) internal onlyInitializing {
-        messageService = _messageService;
+    function __LineaGateway_init() internal onlyInitializing {
+        __BaseGateway_init();
     }
 
     function claimMessage(uint256 _value, bytes calldata _callData, uint256 _nonce) external nonReentrant {

contracts/gateway/linea/LineaL1Gateway.sol

@@ -8,9 +8,13 @@ import {LineaGateway} from "./LineaGateway.sol";
 import {L1BaseGateway} from "../L1BaseGateway.sol";
 
 contract LineaL1Gateway is L1BaseGateway, LineaGateway {
-    function initialize(IArbitrator _arbitrator, IMessageService _messageService) external initializer {
-        __L1BaseGateway_init(_arbitrator);
-        __LineaGateway_init(_messageService);
+    constructor(
+        IArbitrator _arbitrator,
+        IMessageService _messageService
+    ) L1BaseGateway(_arbitrator) LineaGateway(_messageService) {}
+
+    function initialize() external initializer {
+        __LineaGateway_init();
     }
 
     function sendMessage(uint256 _value, bytes memory _callData, bytes memory) external payable onlyArbitrator {

contracts/gateway/linea/LineaL2Gateway.sol

@@ -7,9 +7,13 @@ import {LineaGateway} from "./LineaGateway.sol";
 import {L2BaseGateway} from "../L2BaseGateway.sol";
 
 contract LineaL2Gateway is L2BaseGateway, LineaGateway {
-    function initialize(address _zkLink, IMessageService _messageService) external initializer {
-        __L2BaseGateway_init(_zkLink);
-        __LineaGateway_init(_messageService);
+    constructor(
+        address _zkLink,
+        IMessageService _messageService
+    ) L2BaseGateway(_zkLink) LineaGateway(_messageService) {}
+
+    function initialize() external initializer {
+        __LineaGateway_init();
     }
 
     function sendMessage(uint256 value, bytes memory callData) external payable override onlyZkLink {

contracts/gateway/scroll/ScrollGateway.sol

@@ -7,27 +7,26 @@ import {BaseGateway} from "../BaseGateway.sol";
 
 abstract contract ScrollGateway is BaseGateway, IScrollGateway {
     /// @notice Linea message service on local chain
-    IScrollMessenger public messageService;
+    IScrollMessenger public immutable messageService;
 
     /**
      * @dev This empty reserved space is put in place to allow future versions to add new
      * variables without shifting down storage in the inheritance chain.
      * See https://docs.openzeppelin.com/contracts/4.x/upgradeable#storage_gaps
      */
-    uint256[49] private __gap;
+    uint256[50] private __gap;
 
     /// @dev Modifier to make sure the caller is the known message service.
     modifier onlyMessageService() {
         require(msg.sender == address(messageService), "Not message service");
         _;
     }
 
-    function __ScrollGateway_init(IScrollMessenger _messageService) internal onlyInitializing {
-        __BaseGateway_init();
-        __ScrollGateway_init_unchained(_messageService);
+    constructor(IScrollMessenger _messageService) {
+        messageService = _messageService;
     }
 
-    function __ScrollGateway_init_unchained(IScrollMessenger _messageService) internal onlyInitializing {
-        messageService = _messageService;
+    function __ScrollGateway_init() internal onlyInitializing {
+        __BaseGateway_init();
     }
 }

contracts/gateway/scroll/ScrollL1Gateway.sol

@@ -8,9 +8,13 @@ import {L1BaseGateway} from "../L1BaseGateway.sol";
 import {ScrollGateway} from "./ScrollGateway.sol";
 
 contract ScrollL1Gateway is ScrollGateway, L1BaseGateway {
-    function initialize(IArbitrator _arbitrator, IScrollMessenger _messageService) external initializer {
-        __L1BaseGateway_init(_arbitrator);
-        __ScrollGateway_init(_messageService);
+    constructor(
+        IArbitrator _arbitrator,
+        IScrollMessenger _messageService
+    ) L1BaseGateway(_arbitrator) ScrollGateway(_messageService) {}
+
+    function initialize() external initializer {
+        __ScrollGateway_init();
     }
 
     function sendMessage(

contracts/gateway/scroll/ScrollL2Gateway.sol

@@ -7,9 +7,13 @@ import {L2BaseGateway} from "../L2BaseGateway.sol";
 import {ScrollGateway} from "./ScrollGateway.sol";
 
 contract ScrollL2Gateway is L2BaseGateway, ScrollGateway {
-    function initialize(address _zkLink, IScrollMessenger _messageService) external initializer {
-        __L2BaseGateway_init(_zkLink);
-        __ScrollGateway_init(_messageService);
+    constructor(
+        address _zkLink,
+        IScrollMessenger _messageService
+    ) L2BaseGateway(_zkLink) ScrollGateway(_messageService) {}
+
+    function initialize() external initializer {
+        __ScrollGateway_init();
     }
 
     function sendMessage(uint256 _value, bytes memory _callData) external payable override onlyZkLink {

contracts/gateway/zkpolygon/ZkPolygonL1Gateway.sol

@@ -9,7 +9,7 @@ import {BaseGateway} from "../BaseGateway.sol";
 
 contract ZkPolygonL1Gateway is IZkPolygonGateway, L1BaseGateway, BaseGateway {
     /// @notice ZkPolygon message service on local chain
-    IZkPolygon public messageService;
+    IZkPolygon public immutable messageService;
 
     uint32 public constant ETH_NETWORK_ID = 1;
     // Default to true
@@ -24,13 +24,14 @@ contract ZkPolygonL1Gateway is IZkPolygonGateway, L1BaseGateway, BaseGateway {
     /// @dev Used to indicate that zkSync L2 -> L1 message was already processed
     mapping(uint256 => mapping(uint256 => bool)) public isMessageFinalized;
 
-    function initialize(IArbitrator _arbitrator, IZkPolygon _messageService) external initializer {
-        __L1BaseGateway_init(_arbitrator);
-        __BaseGateway_init();
-
+    constructor(IArbitrator _arbitrator, IZkPolygon _messageService) L1BaseGateway(_arbitrator) {
         messageService = _messageService;
     }
 
+    function initialize() external initializer {
+        __BaseGateway_init();
+    }
+
     function sendMessage(uint256 _value, bytes memory _callData, bytes memory) external payable onlyArbitrator {
         bytes memory executeData = abi.encodeCall(IZkPolygonGateway.claimMessageCallback, (_value, _callData));
         messageService.bridgeMessage{value: msg.value}(

contracts/gateway/zkpolygon/ZkPolygonL2Gateway.sol

@@ -8,7 +8,7 @@ import {BaseGateway} from "../BaseGateway.sol";
 
 contract ZkPolygonL2Gateway is IZkPolygonGateway, L2BaseGateway, BaseGateway {
     /// @notice ZkPolygon message service on local chain
-    IZkPolygon public messageService;
+    IZkPolygon public immutable messageService;
 
     uint32 public constant ETH_NETWORK_ID = 0;
     // Default to true
@@ -19,13 +19,15 @@ contract ZkPolygonL2Gateway is IZkPolygonGateway, L2BaseGateway, BaseGateway {
         require(msg.sender == address(messageService), "Not remote gateway");
         _;
     }
-    function initialize(address _zkLink, IZkPolygon _messageService) external initializer {
-        __L2BaseGateway_init(_zkLink);
-        __BaseGateway_init();
 
+    constructor(address _zkLink, IZkPolygon _messageService) L2BaseGateway(_zkLink) {
         messageService = _messageService;
     }
 
+    function initialize() external initializer {
+        __BaseGateway_init();
+    }
+
     function sendMessage(uint256 _value, bytes memory _callData) external payable onlyZkLink {
         bytes memory executeData = abi.encodeCall(IZkPolygonGateway.claimMessageCallback, (_value, _callData));
         messageService.bridgeMessage{value: msg.value}(

contracts/gateway/zksync/ZkSyncL1Gateway.sol

@@ -11,20 +11,21 @@ import {L2Message} from "../../zksync/l1-contracts/zksync/Storage.sol";
 
 contract ZkSyncL1Gateway is IZkSyncL1Gateway, L1BaseGateway, BaseGateway {
     /// @notice ZkSync message service on local chain
-    IMailbox public messageService;
+    IMailbox public immutable messageService;
 
     /// @dev A mapping L2 batch number => message number => flag
     /// @dev Used to indicate that zkSync L2 -> L1 message was already processed
     mapping(uint256 => mapping(uint256 => bool)) public isMessageFinalized;
 
+    constructor(IArbitrator _arbitrator, IMailbox _messageService) L1BaseGateway(_arbitrator) {
+        messageService = _messageService;
+    }
+
     /// @dev Receive eth from zkSync canonical bridge
     receive() external payable {}
 
-    function initialize(IArbitrator _arbitrator, IMailbox _messageService) external initializer {
-        __L1BaseGateway_init(_arbitrator);
+    function initialize() external initializer {
         __BaseGateway_init();
-
-        messageService = _messageService;
     }
 
     function sendMessage(

contracts/gateway/zksync/ZkSyncL2Gateway.sol

@@ -23,8 +23,9 @@ contract ZkSyncL2Gateway is IZkSyncL2Gateway, L2BaseGateway, BaseGateway {
         _;
     }
 
-    function initialize(address _zkLink) external initializer {
-        __L2BaseGateway_init(_zkLink);
+    constructor(address _zkLink) L2BaseGateway(_zkLink) {}
+
+    function initialize() external initializer {
         __BaseGateway_init();
     }