Web3 & DApp Development Fundamentals · Leçon

Techniques d’optimisation du gaz

Apprenez des stratégies pour écrire un code Solidity économe en gaz, réduire les coûts des transactions et améliorer les performances de vos DApps sur la blockchain.

Techniques d’optimisation du gaz est une leçon Web3 & DApp Development Fundamentals gratuite sur CoddyKit. Ceci est la leçon 3 sur 3. Tu peux lire la leçon complète ci-dessous gratuitement — puis la pratiquer en direct dans le navigateur avec un éditeur de code intégré et un tuteur IA 24/7. Elle fait partie du parcours d'apprentissage Web3 & DApp Development Fundamentals, et ta progression se synchronise sur le web et l'application CoddyKit. Le cours Web3 & DApp Development Fundamentals comprend 3 leçons au total.

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Why Gas Optimization Matters

Welcome to the final lesson in DApp Security & Auditing! Today, we'll master Gas Optimization Techniques.

Gas is the fee paid to execute transactions on the Ethereum network. It's like fuel for your car.

Cost Reduction: Lower gas fees mean cheaper transactions for users.
Performance: Optimized contracts execute faster.
User Experience: Better performance leads to happier users and smoother DApps.

Understanding Gas Costs

Every operation the Ethereum Virtual Machine (EVM) performs costs a certain amount of gas. Complex operations cost more.

When you deploy or interact with a smart contract, you pay gas for:

Storing data on the blockchain (most expensive).
Performing computations.
Sending Ether.

Our goal is to write code that uses fewer of these expensive operations.

Storage vs. Memory vs. Calldata

Understanding where your data lives is key to saving gas. Each location has different costs:

Storage: Permanent, on-chain. Most expensive to read/write (SSTORE/SLOAD).
Memory: Temporary, exists only during function execution. Cheaper than storage.
Calldata: Immutable, read-only, temporary. Used for external function arguments. Cheapest for external inputs.

Prioritize using calldata or memory for variables that don't need to persist on-chain.

Minimize Storage Writes (SSTORE)

Writing to storage (SSTORE) is the single most expensive operation in Solidity. Always ask: does this variable really need to be stored on-chain?

Instead of updating a counter in storage for every iteration, compute it once at the end or use events to log changes.

Consider this simple example:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract StorageCostExample {
    uint256 public counter;

    // High gas cost: writes to storage every call
    function incrementBad() public {
        counter++;
    }

    // Lower gas cost: only reads state
    function getCounter() public view returns (uint256) {
        return counter;
    }
}

Packing Storage Variables

Solidity stores variables in 256-bit (32-byte) 'slots'. If you declare multiple variables that fit within a single slot, they can be 'packed' together, saving gas.

For example, three uint8 variables take up less storage than three uint256 variables if declared consecutively. This saves SSTORE operations.

Declare smaller data types (e.g., uint8, bool) when possible.
Group variables of similar sizes together.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract StoragePacking {
    // These will likely pack into one slot
    uint8 public value1;
    bool public isActive;
    uint8 public value2;

    // This will take a separate slot
    address public owner;

    function setValues(uint8 _v1, bool _active, uint8 _v2) public {
        value1 = _v1;
        isActive = _active;
        value2 = _v2;
    }
}

Short-Circuiting Conditionals

When using logical operators like && (AND) or || (OR), Solidity uses 'short-circuiting'. This means it stops evaluating conditions once the result is known.

You can save gas by placing the cheaper, more likely-to-fail, or more likely-to-be-true conditions first.

For &&, put the condition most likely to be false first.
For ||, put the condition most likely to be true first.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract ShortCircuitExample {
    uint256 public data = 100;

    function checkCondition(uint256 _input) public view returns (bool) {
        // Cheaper check (input) before more expensive check (storage read)
        return (_input > 0 && data > 50); 
    }
}

Efficient Loops & Iterations

Loops can be gas-expensive, especially if they iterate over large arrays stored in storage. Avoid unbounded loops or loops over dynamic arrays in storage when possible.

Process data off-chain if possible.
Use fixed-size arrays instead of dynamic ones if the size is known.
Refactor logic to avoid loops or reduce iterations.
Consider a pull-based system for payouts instead of pushing to many recipients in one transaction.

Using `view` and `pure` Functions

Functions marked as view or pure do not modify the blockchain state. When called externally, they don't cost any gas!

view: Reads state variables but doesn't modify them.
pure: Neither reads nor modifies state variables.

Internal calls to view/pure functions still consume gas (as part of the larger transaction), but using them correctly for external queries is a huge gas saver for users.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract ViewPureExample {
    uint256 public myNumber = 42;

    // Costs no gas for external calls
    function getNumber() public view returns (uint256) {
        return myNumber;
    }

    // Costs no gas for external calls
    function add(uint256 a, uint256 b) public pure returns (uint256) {
        return a + b;
    }
}

Error Handling Gas Costs

Solidity provides several ways to handle errors: require(), revert(), and assert().

require(): Used for validating inputs and conditions. Refunds unused gas when it fails. (Recommended for most checks)
revert(): Similar to require, also refunds unused gas.
assert(): Used for internal invariants and should *never* fail. Consumes ALL remaining gas when it fails. (Use sparingly for critical internal checks)

Failing an assert is much more expensive than failing a require, so choose your error handling wisely.

Question: Gas Optimization

Consider the following Solidity snippet. Which change would likely lead to the MOST significant gas savings for a user calling updateStatus?

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract GasPuzzle {
    uint256 public statusId;
    string public statusName;
    address public owner;

    constructor() {
        owner = msg.sender;
        statusId = 1;
        statusName = "Initial";
    }

    function updateStatus(uint256 _newId, string memory _newName) public {
        require(msg.sender == owner, "Not owner");
        statusId = _newId;
        statusName = _newName;
    }
}

Recap: Gas Optimization Mastery

You've unlocked key strategies for writing gas-efficient Solidity code!

Remember these principles:

Minimize Storage Writes: The golden rule.
Pack Variables: Group smaller variables to fit slots.
Use Efficient Data Locations: Prefer calldata/memory over storage.
Optimize Loops: Avoid unbounded or large iterations.
Leverage view/pure: For gas-free external reads.
Smart Error Handling: Use require/revert, not assert for user input.

Applying these techniques will lead to more affordable, faster, and user-friendly DApps. Keep practicing!

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Toutes les leçons de ce cours

Vulnérabilités courantes des contrats intelligents
Outils et audits de sécurité
Techniques d’optimisation du gaz

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