Efficient Initialization

In Solidity, how you initialize state variables can have a impact on the deployment cost of your contracts, specifically in terms of gas usage. The Ethereum Virtual Machine (EVM) requires gas for every operation, including the initialization of variables.

代码演示

In the example below, we have two contracts, Default and InitDefault. Both contracts declare a state variable foo of type uint256. However, they differ in how foo is initialized:

• Default leaves foo uninitialized, thereby relying on Solidity to set it to the default value of uint256, which is 0.
• InitDefault explicitly initializes foo to 0 during declaration.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

contract Default {
    uint256 foo; // good: 67148 gas
}

contract InitDefault {
    uint256 foo = 0; // bad: 69332 gas
}

When the Default contract is deployed, it uses less gas (67,148 gas) compared to the InitDefault contract (69,332 gas).

The reason behind this difference is that explicitly initializing a variable to its default value generates additional bytecode, which in turn consumes more gas. Solidity's compiler optimizes storage by minimizing the need to explicitly set variables to their default values.

关于 gas 优化的建议：

🌟 If a variable does not need a value other than the default, do not explicitly initialize it. This reduces the contract’s deployment gas cost. While explicitly initializing variables can sometimes enhance code readability by making initial values explicit, it comes at the cost of increased gas.