😎Gas Saving Technique 17: Don’t cache value that is used once

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Introduction

Efficient gas usage is a pivotal consideration for smart contract developers on Ethereum. Sometimes developers cache values into variables for later use, but this might not always be necessary, and it might even result in increased gas consumption. This tutorial will highlight the importance of avoiding unnecessary variable caching, particularly when a value is used only once.

Impact & Details

Unnecessary Variable Caching

• Increased Gas Costs: Creating a variable to store data that is used only once might lead to increased gas costs without any improvement in readability or functionality.

• Avoid Redundant Caching: Be mindful of unnecessary variable assignments, especially when dealing with struct attributes or mappings. Directly accessing values without caching is more gas-efficient when the value is used only once.

Example: Avoiding Unnecessary Variable Caching

Here’s an example demonstrating unnecessary variable caching and its optimized version:

Before Optimization:

solidityCopy code// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract MyContract {
    struct Claim {
        uint256 updated;
        // ... other attributes ...
    }

    mapping(bytes32 => Claim) public claims;

    function someFunction(bytes32 claimIdentifier) public {
        Claim storage claim = claims[claimIdentifier];
        uint256 timestamp = claim.updated;  // Unnecessary variable caching
        // timestamp is used only once in the function
        // ... rest of the function ...
    }
}

After Optimization:

solidityCopy code// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract MyContract {
    struct Claim {
        uint256 updated;
        // ... other attributes ...
    }

    mapping(bytes32 => Claim) public claims;

    function someFunction(bytes32 claimIdentifier) public {
        uint256 timestamp = claims[claimIdentifier].updated;  // Directly accessing value
        // ... rest of the function ...
    }
}

Recommended Mitigation Steps

1. Review Your Smart Contract: Inspect your contract for instances where values are unnecessarily cached into variables.

2. Directly Access Values: If a cached value is used only once, consider accessing it directly instead of storing it in a variable.

3. Test: After making changes, test the contract rigorously to ensure it maintains functionality while utilizing less gas.

Conclusion

Avoiding unnecessary variable caching is a straightforward yet effective technique for gas optimization in smart contracts. For values used only once, direct access is preferable over variable caching. After implementing these changes, always conduct thorough testing to confirm the contract’s functionality and efficiency in gas usage.