🛢️Gas Saving Technique 33: Making Functions Payable for Optimized Gas Costs

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Introduction: In Solidity, function modifiers like onlyOwner ensure that only specific addresses (like the contract's owner) can call certain functions. When unauthorized users call these functions, the transaction reverts. But did you know that marking such functions as payable can lower the gas cost for authorized callers? Let's dive in!

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Concept:

1. Payable Modifier: In Solidity, the payable keyword allows a function to receive Ether. By default, functions reject Ether sent to them to prevent unintentional Ether transfers.

2. Reverting Functions: Functions with access control modifiers (e.g., onlyOwner) revert transactions when called by unauthorized users.

3. Opcodes and Gas: Every operation in the Ethereum Virtual Machine (EVM) costs gas. Certain operations, like checking if a function received Ether (CALLVALUE) and reverting if so, add to the gas cost.

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Examples & Recommendations:

Consider a function with the onlyOwner modifier:

1. Before Optimization:

   solidityCopy codefunction restrictedAction() external onlyOwner {
       // ... perform some action ...
   }

2. After Optimization:

   solidityCopy codefunction restrictedAction() external payable onlyOwner {
       // ... perform some action ...
   }

For unauthorized users, the function will still revert due to the onlyOwner modifier. However, for the owner, the function will be cheaper to call in terms of gas.

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Step-by-Step Guide for Implementing the Payable Optimization:

1. Identification: Scan your contract for functions that have access control modifiers like onlyOwner and are not currently marked as payable.

2. Modification: Update the function definition by adding the payable modifier.

3. Verification: Review each optimized function to ensure that the logic remains intact. Ensure no unintentional Ether transfers can occur.

4. Testing: Thoroughly test the contract. Ensure that functions still behave as expected for both authorized and unauthorized users, and monitor gas costs for improvements.

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Benefits:

1. Gas Savings: Avoiding unnecessary opcodes like CALLVALUE, ISZERO, and REVERT saves an average of about 21 gas per legitimate call to the function. This also reduces deployment costs.

2. Maintained Security: The function's security isn't compromised. Unauthorized calls still revert due to the original access control modifier.

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Conclusion: While Solidity's payable modifier is primarily for enabling Ether transfers to functions, it can also be leveraged to optimize gas costs for functions that revert for standard users. By understanding the underlying opcodes and their gas costs, developers can take advantage of this to create more gas-efficient smart contracts without sacrificing security.