Refs #454 -- Added multicall-in-router.md to general/build/smart-contracts/gas-optimization

docs/general/build/smart-contracts/gas-optimization/multicall-in-router.md

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+displayed_sidebar: generalSidebar
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+
+# Implement multicall in router-like contracts
+
+In Solidity, implementing multicall functionality in router-like contracts can significantly reduce gas costs by batching multiple calls into a single transaction. This is a common feature in contracts like the Uniswap Router and the Compound Bulker. Multicall allows users to execute a sequence of calls within a single transaction, thereby optimizing gas usage and improving efficiency.
+
+**Demo Code**
+
+Below, we have a sample contract `MulticallRouter` that demonstrates how to implement multicall functionality. This contract includes a `multicall` function that accepts an array of encoded function calls and executes them in sequence.
+
+```solidity
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.24;
+
+contract MulticallRouter {
+    function multicall(bytes[] calldata data) external returns (bytes[] memory results) {
+        results = new bytes[](data.length);
+        for (uint256 i = 0; i < data.length; i++) {
+            (bool success, bytes memory result) = address(this).delegatecall(data[i]);
+            require(success, "Multicall execution failed");
+            results[i] = result;
+        }
+    }
+
+    // Example function to demonstrate usage
+    function exampleFunction1(uint256 x) external pure returns (uint256) {
+        return x * 2;
+    }
+
+    function exampleFunction2(uint256 y) external pure returns (uint256) {
+        return y + 3;
+    }
+}
+```
+
+In this example, the `multicall` function uses `delegatecall` to execute each function call in the context of the current contract. This ensures that the state changes and storage modifications occur within the same contract. 
+
+### Usage Example
+
+To use this `MulticallRouter` contract, you can encode the function calls and pass them to the `multicall` function. Here's an example of how to encode and call the functions using Solidity:
+
+```solidity
+contract MulticallExample {
+    MulticallRouter public router;
+
+    constructor(address _router) {
+        router = MulticallRouter(_router);
+    }
+
+    function performMulticall() external {
+        bytes[] memory callData = new bytes[](2);
+        callData[0] = abi.encodeWithSelector(router.exampleFunction1.selector, 42);
+        callData[1] = abi.encodeWithSelector(router.exampleFunction2.selector, 21);
+
+        bytes[] memory results = router.multicall(callData);
+
+        // Handle the results
+        uint256 result1 = abi.decode(results[0], (uint256));
+        uint256 result2 = abi.decode(results[1], (uint256));
+
+        // Do something with the results
+    }
+}
+```
+
+**Gas Optimization Analysis**
+
+The primary advantage of using multicall is the reduction in gas costs by avoiding multiple transaction overheads. Here’s a comparison of gas usage between individual transactions and a single multicall:
+
+- **Individual Transactions**: Each call incurs base transaction costs plus the gas for executing the function.
+- **Single Multicall**: Incurs only one base transaction cost plus the gas for executing each function within a loop.
+
+By batching calls, multicall can significantly reduce the cumulative gas cost, especially when performing multiple operations.
+
+**Recommendations for Gas Optimization**
+
+Implementing multicall in router-like contracts can save gas by reducing the number of transactions and leveraging the lower cumulative gas cost of executing multiple operations in a single transaction.