solidity

solidity

Production smart-contract authoring for EVM chains. Covers the full contract lifecycle: standards compliance, security patterns, gas optimisation, testing with Foundry, and deployment hardening.

Contract Structure

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import {SafeERC20} from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import {ReentrancyGuard} from "@openzeppelin/contracts/utils/ReentrancyGuard.sol";
import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";

contract FlashloanArb is ReentrancyGuard, Ownable {
    using SafeERC20 for IERC20;

    error InsufficientProfit(uint256 expected, uint256 got);
    error UnauthorizedCaller(address caller);

    event ArbExecuted(address indexed asset, uint256 profit, uint256 gasUsed);

    address public immutable POOL;       // Aave V3 Pool
    address public immutable ROUTER;     // Swap router

    constructor(address _pool, address _router) Ownable(msg.sender) {
        POOL   = _pool;
        ROUTER = _router;
    }

    modifier onlyPool() {
        if (msg.sender != POOL) revert UnauthorizedCaller(msg.sender);
        _;
    }
}

Access Control Patterns

Prefer role-based over owner-only for anything beyond toy contracts.

import {AccessControl} from "@openzeppelin/contracts/access/AccessControl.sol";

contract Treasury is AccessControl {
    bytes32 public constant OPERATOR = keccak256("OPERATOR");
    bytes32 public constant EMERGENCY = keccak256("EMERGENCY");

    constructor(address admin) {
        _grantRole(DEFAULT_ADMIN_ROLE, admin);
    }

    function withdraw(address to, uint256 amount) external onlyRole(OPERATOR) { /*...*/ }
    function pause()                              external onlyRole(EMERGENCY) { /*...*/ }
}

Reentrancy Defence

The 2016 DAO hack is still the most common class of exploit. Follow checks-effects-interactions, use ReentrancyGuard on every external-facing state-mutating function that calls untrusted addresses.