update constructor

demo-contract/contracts/wtfswap/Pool.sol

@@ -6,28 +6,33 @@ import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
 import "./interfaces/IFactory.sol";
 
 contract Pool is IPool, ERC20 {
-    function factory() external view override returns (address) {}
-
-    function token0() external view override returns (address) {}
-
-    function token1() external view override returns (address) {}
-
-    function tickLower() external view override returns (int24) {}
-
-    function tickUpper() external view override returns (int24) {}
-
-    function fee() external view override returns (uint24) {}
-
-    function sqrtPriceX96() external view override returns (uint160) {}
-
-    function tick() external view override returns (int24) {}
-
-    function liquidity() external view override returns (uint128) {}
+    /// @inheritdoc IPool
+    address public immutable override factory;
+    /// @inheritdoc IPool
+    address public immutable override token0;
+    /// @inheritdoc IPool
+    address public immutable override token1;
+    /// @inheritdoc IPool
+    uint24 public immutable override fee;
+    /// @inheritdoc IPool
+    int24 public immutable override tickLower;
+    /// @inheritdoc IPool
+    int24 public immutable override tickUpper;
+
+    /// @inheritdoc IPool
+    uint160 public override sqrtPriceX96;
+    /// @inheritdoc IPool
+    int24 public override tick;
+    /// @inheritdoc IPool
+    uint128 public override liquidity;
 
     constructor() {
         ERC20("Wtfswap", "WTF-SWAP");
-        // 调用 IFactory 的 parameters 获取参数
-        (factory, token0, token1, tickLower, tickUpper, fee) = IFactory(
+        // constructor 中初始化 immutable 的常量
+        // Factory 创建 Pool 时会通 new Pool{salt: salt}() 的方式创建 Pool 合约，通过 salt 指定 Pool 的地址，这样其他地方也可以推算出 Pool 的地址
+        // 参数通过读取 Factory 合约的 parameters 获取
+        // 不通过构造函数传入，因为 CREATE2 会根据 initcode 计算出新地址（new_address = hash(0xFF, sender, salt, bytecode)），带上参数就不能计算出稳定的地址了
+        (factory, token0, token1, fee, tickLower, tickUpper) = IFactory(
             msg.sender
         ).parameters();
     }