Fixed-Size/Dynamic Arrays

In Solidity, the way you manage and interact with arrays can impact the gas cost of your smart contract operations. This tutorial demonstrates the difference in gas usage between fixed-size arrays and dynamic arrays when they are filled with values. This understanding can help developers make more cost-effective decisions when designing smart contracts.

Solidity supports two types of arrays: fixed-size arrays and dynamic arrays. Fixed-size arrays have a predefined length and occupy a continuous block of storage, while dynamic arrays can change in size and potentially consume more gas due to the need for resizing and memory allocation.

Demo Code

To illustrate the differences in gas consumption between these two types of arrays, the contract ArrayGasOpt includes two functions: one for filling a dynamic array and another for a fixed-size array.

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

contract ArrayGasOpt {
    uint[] public dynamicArr;
    uint[1000] public staticArr;

    // fill dynamic-length array: 2,224,770 gas
    function fillDynamic() public {
        for(uint i = 0; i < 99; i++) {
            dynamicArr.push(i);
        }
    }

      // fill fixed-length array: 2,182,608 gas
    function fillStatic() public {
        for(uint i = 0; i < 99; i++) {
            staticArr[i] = i;
        }
    }
}

Fixed-size Arrays: These are generally more gas-efficient for storing a large number of elements known at compile time. This is due to the array using a continuous block of storage, which reduces the need for additional memory allocation or resizing.

Dynamic Arrays: While flexible, they can be more costly in terms of gas, especially when frequently resized or when elements are added in a loop. Each push operation might require additional gas to handle memory resizing, depending on the state of the array.

Recommendations for gas optimization:

🌟 When the size of the array is known beforehand and not expected to change, prefer using fixed-size arrays. Use dynamic arrays when you need flexibility in the size of the array.