add periphery immutable state

contracts/NonfungiblePositionManagerV4.sol

@@ -12,21 +12,21 @@ import {Currency} from "@uniswap/v4-core/contracts/types/Currency.sol";
 import {INonfungiblePositionManagerV4} from "./interfaces/INonfungiblePositionManagerV4.sol";
 import {PeripheryValidation} from "./base/PeripheryValidation.sol";
 import {PeripheryPayments} from "./base/PeripheryPayments.sol";
+import {PeripheryImmutableState} from "./base/PeripheryImmutableState.sol";
 import {SelfPermit} from "./base/SelfPermit.sol";
 import {Multicall} from "./base/Multicall.sol";
 
 contract NonfungiblePositionManagerV4 is
     INonfungiblePositionManagerV4,
     ERC721,
+    PeripheryImmutableState,
     PeripheryValidation,
     PeripheryPayments,
     SelfPermit,
     Multicall
 {
     using PoolIdLibrary for PoolKey;
 
-    IPoolManager public immutable poolManager;
-
     error InvalidTokenID();
     error NotApproved();
     error NotCleared();
@@ -68,9 +68,9 @@ contract NonfungiblePositionManagerV4 is
     // TODO: does it still need WETH address in the constructor here?
     // TODO: use ERC721Permit2 here
     constructor(IPoolManager _poolManager, address _tokenDescriptor_)
+        PeripheryImmutableState(_poolManager)
         ERC721("Uniswap V4 Positions NFT-V1", "UNI-V4-POS")
     {
-        poolManager = _poolManager;
         _tokenDescriptor = _tokenDescriptor_;
     }
 

contracts/base/PeripheryImmutableState.sol

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.19;
+
+import {IPoolManager} from "@uniswap/v4-core/contracts/interfaces/IPoolManager.sol";
+import {IPeripheryImmutableState} from "../interfaces/IPeripheryImmutableState.sol";
+
+/// @title Immutable state
+/// @notice Immutable state used by periphery contracts
+abstract contract PeripheryImmutableState is IPeripheryImmutableState {
+    IPoolManager public immutable override poolManager;
+
+    constructor(IPoolManager _poolManager) {
+        poolManager = _poolManager;
+    }
+}

contracts/interfaces/INonfungiblePositionManagerV4.sol

@@ -8,11 +8,18 @@ import {PoolKey} from "@uniswap/v4-core/contracts/types/PoolKey.sol";
 import {Currency} from "@uniswap/v4-core/contracts/types/Currency.sol";
 
 import {IPeripheryPayments} from "./IPeripheryPayments.sol";
+import {IPeripheryImmutableState} from "./IPeripheryImmutableState.sol";
 
 /// @title Non-fungible token for positions
 /// @notice Wraps Uniswap V4 positions in a non-fungible token interface which allows for them to be transferred
 /// and authorized.
-interface INonfungiblePositionManagerV4 is ILockCallback, IPeripheryPayments, IERC721Metadata, IERC721Enumerable {
+interface INonfungiblePositionManagerV4 is
+    ILockCallback,
+    IPeripheryPayments,
+    IPeripheryImmutableState,
+    IERC721Metadata,
+    IERC721Enumerable
+{
     /// @notice Emitted when liquidity is increased for a position NFT
     /// @dev Also emitted when a token is minted
     /// @param tokenId The ID of the token for which liquidity was increased

contracts/interfaces/IPeripheryImmutableState.sol

@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.19;
+
+import {IPoolManager} from "@uniswap/v4-core/contracts/interfaces/IPoolManager.sol";
+
+/// @title Immutable state
+/// @notice Functions that return immutable state
+interface IPeripheryImmutableState {
+    /// @return Returns the pool manager
+    function poolManager() external view returns (IPoolManager);
+}