adding 08 comparing external to public functions

README.md

@@ -122,3 +122,15 @@ It is cheaper to use named return variables and remove explicit `return` stateme
 -    return owners;
 }
 ```
+
+### #8 Use External Instead Of Public Functions: NOT EFFECTIVE ###
+Marking a `public` function as `external` appears to have no effect on gas costs:
+```solidity
+// both implementations cost the same gas
+function resetId(uint256 id) external {
+    idToOwner[id] = address(0);
+}
+function resetId(uint256 id) public {
+    idToOwner[id] = address(0);
+}
+```

src/08-use-ext-func/IdRegUseExtFunc.sol

@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.28;
+
+import {IdRegUnop} from "../IdRegUnop.sol";
+
+contract IdRegUseExtFunc is IdRegUnop {
+    // @audit change from `external` to `public` to see if
+    // gas costs increase (compile breaks the other way)
+    function resetId(uint256 id) public override {
+        idToOwner[id] = address(0);
+    }
+}
+
+

test/05-del-to-def-val/IdRegCalldataArrayInputTest.sol

@@ -6,9 +6,9 @@ import {IdRegDelToDefVal} from "../../src/05-del-to-def-val/IdRegDelToDefVal.sol
 
 // Optimizer ON, 10000 runs
 // ========================
-// Pre  : 979 gas
+// Pre  : 1002 gas
 // forge test --optimizer-runs 10000 --match-contract IdRegUnopTest --match-test test_resetId -vvv
-// Post : 979 gas (no improvement)
+// Post : 1002 gas (no improvement)
 // forge test --optimizer-runs 10000 --match-contract IdRegDelToDefVal --match-test test_resetId -vvv
 //
 // Optimizer OFF

test/08-use-ext-func/IdRegUseExtFuncTest.sol

@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.28;
+
+import {IdRegUnopTest} from "../IdRegUnopTest.sol";
+import {IdRegUseExtFunc} from "../../src/08-use-ext-func/IdRegUseExtFunc.sol";
+
+// Optimizer ON, 10000 runs
+// ========================
+// Pre  : 1002 gas
+// forge test --optimizer-runs 10000 --match-contract IdRegUnopTest --match-test test_resetId -vvv
+// Post : 1002 gas (no improvement)
+// forge test --optimizer-runs 10000 --match-contract IdRegUseExtFuncTest --match-test test_resetId -vvv
+//
+// Optimizer OFF
+// =============
+// Pre  : 1018 gas
+// forge test --match-contract IdRegUnopTest --match-test test_resetId -vvv
+// Post : 1018 gas (no improvement)
+// forge test --match-contract IdRegUseExtFuncTest --match-test test_resetId -vvv
+//
+// Conclusion
+// ==========
+// Setting storage to default values costs the same
+// as using the `delete` keyword
+contract IdRegUseExtFuncTest is IdRegUnopTest {
+    function setUp() external override {
+        idReg = new IdRegUseExtFunc();
+    }
+}