Overview
Solidity is the primary language for Ethereum smart contracts. It compiles to EVM bytecode that runs on Ethereum and all EVM-compatible chains. This skill covers contract structure, common patterns (ERC-20, ERC-721), security, and deployment with Hardhat/Foundry.
Instructions
Step 1: Basic Contract
solidity
// contracts/SimpleStorage.sol — Basic smart contract
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;
contract SimpleStorage {
uint256 private value;
address public owner;
event ValueChanged(uint256 newValue, address changedBy);
modifier onlyOwner() {
require(msg.sender == owner, "Not owner");
_;
}
constructor(uint256 initialValue) {
owner = msg.sender;
value = initialValue;
}
function setValue(uint256 newValue) external onlyOwner {
value = newValue;
emit ValueChanged(newValue, msg.sender);
}
function getValue() external view returns (uint256) {
return value;
}
}
Step 2: ERC-20 Token
solidity
// contracts/MyToken.sol — Standard ERC-20 token
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
contract MyToken is ERC20, Ownable {
constructor() ERC20("My Token", "MTK") Ownable(msg.sender) {
_mint(msg.sender, 1_000_000 * 10 ** decimals()); // 1M tokens
}
function mint(address to, uint256 amount) external onlyOwner {
_mint(to, amount);
}
}
Step 3: Deploy with Hardhat
bash
npm install --save-dev hardhat @nomicfoundation/hardhat-toolbox
npx hardhat init
typescript
// scripts/deploy.ts — Deploy contract
import { ethers } from 'hardhat'
async function main() {
const Token = await ethers.getContractFactory('MyToken')
const token = await Token.deploy()
await token.waitForDeployment()
console.log('Token deployed to:', await token.getAddress())
}
main()
bash
npx hardhat compile
npx hardhat test
npx hardhat run scripts/deploy.ts --network sepolia
Step 4: Foundry (Alternative)
bash
forge init my-project
forge build
forge test
forge script script/Deploy.s.sol --rpc-url sepolia --broadcast
Guidelines
- Always use OpenZeppelin contracts for standards (ERC-20, ERC-721) — battle-tested and audited.
- Common vulnerabilities: reentrancy, integer overflow (fixed in 0.8+), front-running, access control.
- Test thoroughly — deployed contracts are immutable. Use Hardhat or Foundry for testing.
- Foundry is faster for compilation/testing (Rust-based). Hardhat has a larger plugin ecosystem.