Library contracts in Blockchain / Solidity - Mini Project: Build & Apply

Library Contracts

📖 Scenario: You are building a simple blockchain project where you want to reuse common functions across multiple smart contracts. Instead of copying code, you will create a library contract that other contracts can call. This helps keep your code clean and efficient.

🎯 Goal: Create a library contract with a function to add two numbers. Then create a main contract that uses this library to add two numbers and show the result.

📋 What You'll Learn

Create a library contract named MathLib with a function add(uint a, uint b) returns (uint) that returns the sum of a and b.

Create a contract named Calculator that uses MathLib to add two numbers.

In Calculator, create a function calculateSum(uint x, uint y) returns (uint) that calls MathLib.add and returns the result.

Write a function to get the sum and print it.

💡 Why This Matters

🌍 Real World

Library contracts help developers reuse common code in blockchain projects, making smart contracts smaller and easier to maintain.

💼 Career

Understanding library contracts is important for blockchain developers to write efficient and modular smart contracts used in decentralized applications.

1

Create the library contract

Create a library contract called MathLib with a public function add that takes two uint parameters a and b and returns their sum as uint.

Blockchain / Solidity

// Your code here to create the MathLib library contract

Need a hint?

Use the library keyword to create a library contract. The add function should be public and pure because it does not change or read state.

2

Create the main contract and import the library

Create a contract called Calculator. Inside it, add a function calculateSum that takes two uint parameters x and y. This function will use MathLib.add to add the two numbers and return the result.

Blockchain / Solidity

library MathLib {
    function add(uint a, uint b) public pure returns (uint) {
        return a + b;
    }
}

// Your code here to create the Calculator contract

Need a hint?

Define the Calculator contract and inside it create the calculateSum function. Call the library function using MathLib.add(x, y).

3

Add a function to call and print the sum

Inside the Calculator contract, add a public function called getSum that calls calculateSum with the numbers 5 and 7 and returns the result.

Blockchain / Solidity

library MathLib {
    function add(uint a, uint b) public pure returns (uint) {
        return a + b;
    }
}

contract Calculator {
    function calculateSum(uint x, uint y) public pure returns (uint) {
        return MathLib.add(x, y);
    }

    // Your code here to add getSum function
}

Need a hint?

Create a simple function getSum that calls calculateSum with fixed numbers and returns the result.

4

Print the result of the sum

Write a line of code to call getSum() from the Calculator contract and print the result.

Blockchain / Solidity

library MathLib {
    function add(uint a, uint b) public pure returns (uint) {
        return a + b;
    }
}

contract Calculator {
    function calculateSum(uint x, uint y) public pure returns (uint) {
        return MathLib.add(x, y);
    }

    function getSum() public pure returns (uint) {
        return calculateSum(5, 7);
    }
}

// Your code here to print the result of getSum()

Need a hint?

Solidity contracts do not print like normal programs. You get the result by calling the function from outside the contract (like a test or blockchain interface). The sum of 5 and 7 is 12.