Reference types behavior in Blockchain / Solidity - Mini Project: Build & Apply

Understanding Reference Types Behavior in Blockchain Smart Contracts

📖 Scenario: Imagine you are building a simple blockchain smart contract to manage a list of users and their balances. You want to understand how reference types like arrays behave when you assign them to new variables or modify them inside functions.

🎯 Goal: You will create a smart contract that stores an array of balances. You will then create a function to demonstrate how modifying a reference type affects the original data. This will help you understand reference types behavior in Solidity.

📋 What You'll Learn

Create a balances array with initial values

Create a tempBalances variable to hold a reference to balances

Write a function to modify tempBalances and observe changes in balances

Print the balances before and after modification

💡 Why This Matters

🌍 Real World

Understanding reference types is important when writing smart contracts that manage data efficiently and correctly on the blockchain.

💼 Career

Blockchain developers must know how data is stored and modified in smart contracts to avoid bugs and security issues.

1

Create the initial balances array

Create a public uint[] array called balances with these exact values: 100, 200, and 300.

Blockchain / Solidity

// Create a public uint[] array called balances with values 100, 200, 300
// Your code here

Need a hint?

Use uint[] public balances = [100, 200, 300]; inside the contract.

2

Create a reference variable to balances

Inside the contract, create a public function called setTempBalances that declares a local uint[] storage variable named tempBalances and assign it to balances.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract ReferenceTypes {
    uint[] public balances = [100, 200, 300];

    // Create setTempBalances function and assign tempBalances to balances
    // Your code here
}

Need a hint?

Use uint[] storage tempBalances = balances; inside the function.

3

Modify the reference variable

Inside the setTempBalances function, add code to change the first element of tempBalances to 999.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract ReferenceTypes {
    uint[] public balances = [100, 200, 300];

    function setTempBalances() public {
        uint[] storage tempBalances = balances;
        // Change the first element of tempBalances to 999
        // Your code here
    }
}

Need a hint?

Use tempBalances[0] = 999; to modify the first element.

4

Check the updated balances

Add a public view function called getBalances that returns the balances array. This will show the updated balances after calling setTempBalances.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract ReferenceTypes {
    uint[] public balances = [100, 200, 300];

    function setTempBalances() public {
        uint[] storage tempBalances = balances;
        tempBalances[0] = 999;
    }

    // Create getBalances function to return balances
    // Your code here
}

Need a hint?

Use function getBalances() public view returns (uint[] memory) { return balances; }.