Packing variables for gas savings in Blockchain / Solidity - Mini Project: Build & Apply

Packing variables for gas savings

📖 Scenario: You are creating a smart contract on Ethereum. You want to store user data efficiently to save gas fees when users interact with your contract.

🎯 Goal: Build a Solidity contract that packs multiple small variables into a single storage slot to reduce gas costs.

📋 What You'll Learn

Create a Solidity contract named UserData

Declare three variables: uint8 age, bool isMember, and uint16 score

Pack these variables into a single uint256 storage variable named packedData

Write a function packData(uint8 age, bool isMember, uint16 score) to store the packed data

Write a function unpackData() that returns the original age, isMember, and score

💡 Why This Matters

🌍 Real World

Packing variables reduces the amount of storage used in smart contracts, which lowers gas fees for users interacting with the contract.

💼 Career

Understanding gas optimization techniques like variable packing is important for blockchain developers to write efficient and cost-effective smart contracts.

1

Create the contract and declare variables

Create a Solidity contract named UserData and declare three state variables: uint8 age, bool isMember, and uint16 score.

Blockchain / Solidity

contract UserData {
    // Declare variables here
}

Need a hint?

Use contract UserData { } to start. Declare each variable inside the contract.

2

Add a packed storage variable

Inside the UserData contract, declare a single uint256 state variable named packedData to hold all packed values.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract UserData {
    uint8 age;
    bool isMember;
    uint16 score;
    // Declare packedData here
}

Need a hint?

Use uint256 packedData; inside the contract.

3

Write the packData function

Write a public function packData(uint8 age, bool isMember, uint16 score) that packs the three variables into packedData using bit shifting and bitwise OR operations.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract UserData {
    uint8 age;
    bool isMember;
    uint16 score;
    uint256 packedData;

    // Write packData function here
}

Need a hint?

Use bit shifting: age at bits 0-7, isMember at bit 8, score at bits 9-24.

4

Write the unpackData function and print results

Write a public view function unpackData() that returns age, isMember, and score by extracting them from packedData using bitwise operations. Then, add a function printData() that returns a string showing the unpacked values.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract UserData {
    uint8 age;
    bool isMember;
    uint16 score;
    uint256 packedData;

    function packData(uint8 _age, bool _isMember, uint16 _score) public {
        packedData = uint256(_age);
        packedData |= (uint256(_isMember ? 1 : 0) << 8);
        packedData |= (uint256(_score) << 9);
    }

    // Write unpackData and printData functions here
}

Need a hint?

Use bit masks and shifts to extract each value. Use a helper function to convert numbers to strings for printing.