Gas optimization for L2 in Blockchain / Solidity - Mini Project: Build & Apply

Gas Optimization for Layer 2 Blockchain Transactions

📖 Scenario: You are developing a smart contract that will run on a Layer 2 (L2) blockchain solution. L2 solutions help reduce gas fees and increase transaction speed compared to Layer 1 (L1) blockchains. However, writing efficient smart contract code is still important to minimize gas costs.In this project, you will create a simple contract that stores user balances and allows deposits and withdrawals. You will then optimize the contract code to reduce gas usage by applying common gas-saving techniques.

🎯 Goal: Build a smart contract that manages user balances with deposit and withdrawal functions. Then optimize the contract to reduce gas consumption by using efficient data types, minimizing storage writes, and using unchecked math where safe.

📋 What You'll Learn

Create a mapping to store user balances

Add a deposit function to increase user balance

Add a withdraw function to decrease user balance

Optimize the contract to reduce gas usage

💡 Why This Matters

🌍 Real World

Layer 2 blockchains are used to make blockchain transactions faster and cheaper. Writing gas-efficient smart contracts helps users save money and improves network performance.

💼 Career

Blockchain developers must optimize smart contracts for gas efficiency to build scalable decentralized applications and reduce costs for users.

1

Create the initial balance mapping

Create a Solidity contract named GasOptimizedL2 and inside it, declare a public mapping called balances that maps address to uint256.

Blockchain / Solidity

contract GasOptimizedL2 {
    // Your code here
}

Need a hint?

Use mapping(address => uint256) public balances; inside the contract.

2

Add deposit and withdraw functions

Add two public functions inside GasOptimizedL2: deposit and withdraw. The deposit function should accept a uint256 amount and add it to balances[msg.sender]. The withdraw function should accept a uint256 amount and subtract it from balances[msg.sender] only if the balance is sufficient.

Blockchain / Solidity

contract GasOptimizedL2 {
    mapping(address => uint256) public balances;

    // Your code here
}

Need a hint?

Use balances[msg.sender] += amount; in deposit and check balance with require in withdraw.

3

Optimize gas usage in withdraw function

Modify the withdraw function to use an unchecked block when subtracting amount from balances[msg.sender] to save gas, since the require already ensures no underflow.

Blockchain / Solidity

contract GasOptimizedL2 {
    mapping(address => uint256) public balances;

    function deposit(uint256 amount) public {
        balances[msg.sender] += amount;
    }

    function withdraw(uint256 amount) public {
        require(balances[msg.sender] >= amount, "Insufficient balance");
        // Your code here
    }
}

Need a hint?

Wrap the subtraction inside unchecked { ... } to save gas.

4

Print final contract code

Print the entire GasOptimizedL2 contract code to verify your final optimized contract.

Blockchain / Solidity

contract GasOptimizedL2 {
    mapping(address => uint256) public balances;

    function deposit(uint256 amount) public {
        balances[msg.sender] += amount;
    }

    function withdraw(uint256 amount) public {
        require(balances[msg.sender] >= amount, "Insufficient balance");
        unchecked {
            balances[msg.sender] -= amount;
        }
    }
}

// Your code here to print the contract code

Need a hint?

Since Solidity contracts are not printed at runtime, confirm your final code matches the optimized contract.