Solidity Smart Contract Patterns

2. Contract structure canonique

// SPDX-License-Identifier: MIT
pragma solidity 0.8.26;

import {ERC20} from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import {Ownable2Step} from "@openzeppelin/contracts/access/Ownable2Step.sol";
import {ReentrancyGuard} from "@openzeppelin/contracts/utils/ReentrancyGuard.sol";

contract MyToken is ERC20, Ownable2Step, ReentrancyGuard {
    // === Custom errors (gas-cheap vs require strings) ===
    error ZeroAddress();
    error InsufficientBalance(uint256 requested, uint256 available);
    error TransferFailed();

    // === Events ===
    event TokensWithdrawn(address indexed user, uint256 amount);

    // === Immutable state (gas-cheap, set in constructor) ===
    uint256 public immutable maxSupply;

    // === Storage ===
    mapping(address account => uint256 lastClaim) public lastClaims;

    constructor(uint256 _maxSupply, address _owner)
        ERC20("MyToken", "MTK")
        Ownable(_owner)
    {
        if (_owner == address(0)) revert ZeroAddress();
        maxSupply = _maxSupply;
    }

    function mint(address to, uint256 amount) external onlyOwner {
        if (totalSupply() + amount > maxSupply) {
            revert InsufficientBalance({requested: amount, available: maxSupply - totalSupply()});
        }
        _mint(to, amount);
    }

    // === Withdrawal pattern ===
    function withdraw() external nonReentrant {
        uint256 amount = pendingWithdrawals[msg.sender];
        if (amount == 0) revert InsufficientBalance(0, 0);

        // CEI: Checks-Effects-Interactions
        pendingWithdrawals[msg.sender] = 0;
        emit TokensWithdrawn(msg.sender, amount);

        (bool success, ) = msg.sender.call{value: amount}("");
        if (!success) revert TransferFailed();
    }

    mapping(address => uint256) public pendingWithdrawals;
}

3. ERC-721 NFT collection

// SPDX-License-Identifier: MIT
pragma solidity 0.8.26;

import {ERC721} from "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import {ERC721Royalty} from "@openzeppelin/contracts/token/ERC721/extensions/ERC721Royalty.sol";
import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";

contract MyCollection is ERC721, ERC721Royalty, Ownable {
    uint256 public constant MAX_SUPPLY = 10_000;
    uint256 public constant MINT_PRICE = 0.01 ether;
    uint256 public nextTokenId = 1;
    string private _baseTokenURI;

    error MaxSupplyReached();
    error InsufficientPayment();

    constructor(string memory baseURI, address royaltyReceiver, uint96 royaltyBps)
        ERC721("MyCollection", "MYC")
        Ownable(msg.sender)
    {
        _baseTokenURI = baseURI;
        _setDefaultRoyalty(royaltyReceiver, royaltyBps);  // EIP-2981
    }

    function mint() external payable {
        if (nextTokenId > MAX_SUPPLY) revert MaxSupplyReached();
        if (msg.value < MINT_PRICE) revert InsufficientPayment();

        uint256 tokenId = nextTokenId++;
        _safeMint(msg.sender, tokenId);
    }

    function _baseURI() internal view override returns (string memory) {
        return _baseTokenURI;
    }

    function setBaseURI(string calldata baseURI) external onlyOwner {
        _baseTokenURI = baseURI;
    }

    function withdraw() external onlyOwner {
        (bool ok, ) = owner().call{value: address(this).balance}("");
        require(ok, "Withdraw failed");
    }

    function supportsInterface(bytes4 interfaceId)
        public view override(ERC721, ERC721Royalty)
        returns (bool)
    {
        return super.supportsInterface(interfaceId);
    }
}

4. Upgrade patterns

UUPS (recommandé en 2026)

import {Initializable} from "@openzeppelin/contracts-upgradeable/proxy/utils/Initializable.sol";
import {UUPSUpgradeable} from "@openzeppelin/contracts-upgradeable/proxy/utils/UUPSUpgradeable.sol";
import {OwnableUpgradeable} from "@openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol";

contract MyContractV1 is Initializable, OwnableUpgradeable, UUPSUpgradeable {
    uint256 public counter;

    function initialize(address _owner) public initializer {
        __Ownable_init(_owner);
        __UUPSUpgradeable_init();
    }

    function increment() external {
        counter += 1;
    }

    function _authorizeUpgrade(address newImplementation) internal override onlyOwner {}
}

Déploiement avec forge script + OpenZeppelin Upgrades :

import {Upgrades} from "openzeppelin-foundry-upgrades/Upgrades.sol";

address proxy = Upgrades.deployUUPSProxy(
    "MyContractV1.sol",
    abi.encodeCall(MyContractV1.initialize, (owner))
);

Important : pour les upgrades, le storage layout est critique. Toujours vérifier avec forge inspect et OZ Upgrades plugin.

5. Tests Foundry

Tests unitaires

// SPDX-License-Identifier: MIT
pragma solidity 0.8.26;

import {Test, console2} from "forge-std/Test.sol";
import {MyToken} from "../src/MyToken.sol";

contract MyTokenTest is Test {
    MyToken token;
    address owner = makeAddr("owner");
    address alice = makeAddr("alice");

    function setUp() public {
        token = new MyToken(1_000_000 ether, owner);
    }

    function test_Mint() public {
        vm.prank(owner);
        token.mint(alice, 100 ether);
        assertEq(token.balanceOf(alice), 100 ether);
    }

    function test_RevertWhen_NonOwnerMints() public {
        vm.expectRevert();
        vm.prank(alice);
        token.mint(alice, 100 ether);
    }

    function test_RevertWhen_ExceedsMaxSupply() public {
        vm.prank(owner);
        vm.expectRevert(abi.encodeWithSelector(
            MyToken.InsufficientBalance.selector, 2_000_000 ether, 1_000_000 ether
        ));
        token.mint(alice, 2_000_000 ether);
    }
}

Fuzz tests

function testFuzz_Mint(address to, uint96 amount) public {
    vm.assume(to != address(0));
    vm.assume(amount > 0 && amount <= 1_000_000 ether);

    vm.prank(owner);
    token.mint(to, amount);
    assertEq(token.balanceOf(to), amount);
}

Invariant tests

contract MyTokenInvariants is Test {
    MyToken token;

    function setUp() public {
        token = new MyToken(1_000_000 ether, address(this));
    }

    function invariant_TotalSupplyNeverExceedsMax() public view {
        assertLe(token.totalSupply(), token.maxSupply());
    }
}

6. Gas optimization techniques

Storage packing

// BAD: 3 storage slots
struct UserBad {
    uint256 balance;     // slot 0
    uint8 level;         // slot 1 (gaspille 31 bytes)
    address account;     // slot 2
}

// GOOD: 2 storage slots
struct UserGood {
    address account;     // slot 0 (20 bytes)
    uint8 level;         // slot 0 (1 byte, packé)
    uint96 balance;      // slot 0 (12 bytes, packé)
                         // total: 33 bytes → ne tient pas, donc balance va sur slot 1
}
// Better:
struct UserBest {
    uint128 balance;     // slot 0 (16 bytes)
    address account;     // slot 0 (20 bytes) → trop, donc account va sur slot 1
    uint8 level;         // slot 1 (avec account)
}

Constant vs immutable

uint256 public constant FEE_BPS = 100;       // gravé dans le bytecode
address public immutable owner;              // assigné au constructor, lecture cheap
uint256 public storageCounter;                // SLOAD coûteux

Calldata vs memory

// BAD: copy memory inutile
function processBad(uint256[] memory data) external { /* ... */ }

// GOOD: read directly from calldata
function processGood(uint256[] calldata data) external { /* ... */ }

Unchecked blocks (Solidity 0.8.x)

function safeIncrement(uint256[] memory arr) public pure {
    uint256 len = arr.length;
    for (uint256 i; i < len;) {
        arr[i] += 1;
        unchecked { ++i; }  // safe: i ne peut pas overflow car borné par len
    }
}

Custom errors > require strings

// BAD: ~50 gas par char + storage du string
require(amount > 0, "Amount must be positive");

// GOOD: ~50 gas total
error AmountMustBePositive();
if (amount == 0) revert AmountMustBePositive();

7. Event-driven architecture (The Graph)

event Transfer(address indexed from, address indexed to, uint256 amount);
event UserCreated(address indexed user, uint256 timestamp, string metadata);

indexed permet de filter sur cette propriété dans The Graph et les RPC eth_getLogs.

Sans events, la seule façon de query l'historique est de re-scanner toute la chaîne — impraticable. Les events sont la façon canonique de communiquer avec le off-chain.

8. Anti-patterns critiques

1. Pas de nonReentrant sur les fonctions qui font des call externes → reentrancy attacks (The DAO, Cream Finance, etc.)
2. Violer le pattern CEI → state non-cohérent en cas de revert
3. Send ETH avec transfer() ou send() → 2300 gas stipend insuffisant pour les nouveaux contracts. Utiliser call{value: x}("") avec check de retour
4. tx.origin au lieu de msg.sender → phishing facile
5. Pas de tests fuzz sur les calculs financiers → bugs subtils
6. Block timestamps comme source de hasard → manipulables par les miners
7. Storage layout cassé après upgrade → corruption de state
8. Ownable simple au lieu de Ownable2Step → erreur de transfert irrécupérable
9. Pas de unchecked dans les loops bornés → 30 gas perdu par itération
10. require(success) sans message → debug impossible
11. Public state sans _ prefix pour l'internal → confusion lectures
12. Pas de timelock sur les upgrades en production → centralisation
13. Hardcoded gas limit dans call{gas: 2300} → casse à la prochaine hard fork
14. Pas d'audit avant mainnet → tu vas perdre les funds

Checklist livraison

• Solidity 0.8.x ou plus
• OpenZeppelin Contracts last stable
• Tous les external payable ont nonReentrant ou justifient leur absence
• Custom errors plutôt que require strings
• Events sur tous les state changes critiques
• Storage packing optimisé
• immutable / constant partout où c'est possible
• Tests unitaires + fuzz + invariants
• Coverage >= 90%
• Gas snapshot dans la CI (forge snapshot --diff)
• Slither + Mythril en CI
• Audit externe avant mainnet
• Timelock + multisig sur les fonctions admin
• Verified sur Etherscan post-deploy

Quand déléguer

• Sécurité smart contract → skill smart-contract-security (ce plugin)
• Intégration off-chain (frontend, indexer) → skill web3-integration (ce plugin)
• Choix architectural blockchain → agent blockchain-expert (ce plugin)
• Déploiement multi-chain → workflows custom

Ressources

• https://book.getfoundry.sh/
• https://docs.openzeppelin.com/contracts/
• https://swcregistry.io/ (Smart Contract Weakness Classification)
• https://consensys.github.io/smart-contract-best-practices/