Storage vs memory vs calldata in Blockchain / Solidity - Hands-On Comparison

Understanding Storage, Memory, and Calldata in Solidity

📖 Scenario: Imagine you are building a simple smart contract for a blockchain-based voting system. You need to understand how to store and handle data efficiently using storage, memory, and calldata in Solidity.

🎯 Goal: You will create a Solidity contract that stores candidates in storage, uses memory to handle temporary data inside functions, and uses calldata to accept input parameters efficiently.

📋 What You'll Learn

Create a string[] array called candidates stored in storage

Create a function addCandidate that accepts a string parameter using calldata and adds it to candidates

Create a function getCandidateCopy that returns a copy of a candidate's name using memory

Print the candidate's name from getCandidateCopy to demonstrate the output

💡 Why This Matters

🌍 Real World

Smart contracts on blockchains need to manage data efficiently to save gas and work correctly. Understanding where data lives helps developers write better contracts.

💼 Career

Blockchain developers must know how to use <code>storage</code>, <code>memory</code>, and <code>calldata</code> to optimize smart contracts for performance and cost.

1

Create the candidates array in storage

Create a public string[] array called candidates that is stored in storage inside the contract.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Voting {
    // Create public string array candidates in storage
    // Your code here
}

Need a hint?

Use string[] public candidates; inside the contract to create a storage array.

2

Add a candidate using calldata parameter

Create a public function called addCandidate that takes a string calldata parameter named name and adds it to the candidates array.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Voting {
    string[] public candidates;

    // Create addCandidate function with string calldata name parameter
    // Your code here
}

Need a hint?

Use string calldata name to accept the input efficiently and candidates.push(name); to add it.

3

Return a candidate's name using memory

Create a public view function called getCandidateCopy that takes a uint parameter index and returns a string memory copy of the candidate's name at that index.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Voting {
    string[] public candidates;

    function addCandidate(string calldata name) public {
        candidates.push(name);
    }

    // Create getCandidateCopy function returning string memory
    // Your code here
}

Need a hint?

Use string memory as the return type to return a copy of the candidate's name.

4

Print the candidate's name from getCandidateCopy

Add a public function called printCandidate that takes a uint parameter index, calls getCandidateCopy with that index, and returns the candidate's name as a string.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Voting {
    string[] public candidates;

    function addCandidate(string calldata name) public {
        candidates.push(name);
    }

    function getCandidateCopy(uint index) public view returns (string memory) {
        return candidates[index];
    }

    // Create printCandidate function that returns string
    // Your code here
}

Need a hint?

Call getCandidateCopy inside printCandidate and return the result.