Constant Rule

Use constant whenever you can. The value is embedded to the bytecode of the contract when you use constant, this saves gas because we don’t make any cold storage read.

Example

pragma solidity ^0.8.17;

contract Constants {
    address constant constantRouter = 0xe592427a0aece92de3edee1f18e0157c05861564;
    address public storageRouter = 0xe592427a0aece92de3edee1f18e0157c05861564;

    function getConstant() external pure returns (address) {
        return constantRouter;
    }

    function getStorage() external view returns (address) {
        return storageRouter;
    }
}

Calling function getStorage would cost 136 gas and calling function getConstant would cost 18 gas only, proving that using constant variables help saves almost seven times the gas cost.

Test Environment

• Compiler: solc 0.8.17
• Testing Framework: Foundry

ETH saved over 100 transactions

100 tx * 30 gwei * 0.000000001 * (136-18) = 0.000354 ~= 0.0004 ETH¹

USD Saved over 100 transactions

• At \$4000 / ETH: \$1.6
• At \$3000/ETH: \$1.2
• At \$2000/ETH: \$0.8