Lesson 9 - MyERC20.sol and MyERC721.sol

Quickstart with OpenZeppelin wizard

• Overview about Ethereum Improvement Proposals (EIPs)
• Overview about Application-level standards and conventions (ERCs)
• Explain about OpenZeppelin Contracts library
• (Review) Objects in smart contracts
• Inheritance overview
• Overview about ERC20
• Overview about ERC721
• Using OpenZeppelin wizard

References

https://eips.ethereum.org/

https://eips.ethereum.org/erc

https://docs.openzeppelin.com/contracts/5.x/

https://docs.openzeppelin.com/contracts/5.x/erc20

https://docs.openzeppelin.com/contracts/5.x/erc721

https://docs.soliditylang.org/en/latest/contracts.html#inheritance

https://solidity-by-example.org/inheritance/

https://docs.openzeppelin.com/contracts/5.x/wizard

https://docs.openzeppelin.com/contracts/5.x/backwards-compatibility

Installation

npm install --save-dev @openzeppelin/contracts

or

yarn add --dev @openzeppelin/contracts

or

bun add -d @openzeppelin/contracts

Plain ERC20 Code reference

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract MyToken is ERC20 {
    constructor() ERC20("MyToken", "MTK") {}
}

Plain ERC721 Code reference

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

contract MyNFT is ERC721 {
    constructor() ERC721("MyNFT", "NFT") {}
}

Contract structure

• Syntax about inheritance
• Overview about OpenZeppelin features for ERC20 and ERC721
• Overview about OpenZeppelin features for Access Control
• Overview about OpenZeppelin utilities and components
• Adding minting feature
• Adding RBAC feature

References

https://www.npmjs.com/package/@openzeppelin/contracts

https://docs.openzeppelin.com/contracts/5.x/extending-contracts

https://docs.openzeppelin.com/contracts/5.x/access-control

Operating the contracts with scripts

• (Review) Script operation
• (Review) Accounts and funding
• (Review) Providers
• (Review) Async operations
• (Review) Running scripts on test environment
• (Review) Contract factory and json imports
• (Review) Transaction receipts and async complexities when running onchain

Code reference

• Script structure

import { viem } from "hardhat";
import { parseEther } from "viem";

async function main() {
    const publicClient = await viem.getPublicClient();
    const [deployer, account1, account2] = await viem.getWalletClients();
    // TODO
}

main().catch((err) => {
  console.error(err);
  process.exitCode = 1;
});

• Deploying with hardhat helper functions

const tokenContract = await viem.deployContract("MyToken");
console.log(`Contract deployed at ${tokenContract.address}`);

• Fetching total supply

const totalSupply = await tokenContract.read.totalSupply();
console.log({ totalSupply });

• Implementing initial supply

    constructor() ERC20("MyToken", "MTK") {
        _mint(msg.sender, 10 * 10 ** decimals());
    }

• Implementing RBAC for supply control

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/AccessControl.sol";

contract MyToken is ERC20, AccessControl {
    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");

    constructor() ERC20("MyToken", "MTK") {
        _mint(msg.sender, 10 * 10 ** decimals());
        _grantRole(DEFAULT_ADMIN_ROLE, msg.sender);
    }

    function mint(address to, uint256 amount) public onlyRole(MINTER_ROLE) {
        _mint(to, amount);
    }
}

• Handling roles

// Fetching the role code
const code = await tokenContract.read.MINTER_ROLE();

• Minting tokens without role fails

const mintTx = await tokenContract.write.mint(
    [deployer.account.address, parseEther("10")],
    { account: account2.account }
);
await publicClient.waitForTransactionReceipt({ hash: mintTx });

This should fail with the error AccessControlUnauthorizedAccount

• Minting tokens with the proper Minter Role

// Giving role
const roleTx = await tokenContract.write.grantRole([
  code,
  account2.account.address,
]);
await publicClient.waitForTransactionReceipt({ hash: roleTx });

• Fetching token data with Promise.all()

const [name, symbol, decimals, totalSupply] = await Promise.all([
  tokenContract.read.name(),
  tokenContract.read.symbol(),
  tokenContract.read.decimals(),
  tokenContract.read.totalSupply(),
]);
console.log({ name, symbol, decimals, totalSupply });

• Sending a transaction

// Sending a transaction
const tx = await tokenContract.write.transfer([
  account1.account.address,
  parseEther("2"),
]);
await publicClient.waitForTransactionReceipt({ hash: tx });

• Viewing balances

const myBalance = await tokenContract.read.balanceOf([deployer.account.address]);
console.log(`My Balance is ${myBalance} decimals units`);
const otherBalance = await tokenContract.read.balanceOf([account1.account.address]);
console.log(
  `The Balance of Acc1 is ${otherBalance} decimals units`
);

• Viewing converted balances

import { parseEther, formatEther } from "viem";
...
const myBalance = await tokenContract.read.balanceOf([deployer.account.address]);
console.log(`My Balance is ${formatEther(myBalance)} ${symbol}`);
const otherBalance = await tokenContract.read.balanceOf([account1.account.address]);
console.log(
  `The Balance of Acc1 is ${formatEther(otherBalance)} ${symbol}`
);

• Viewing converted balances with decimals conversion

function decimals() public pure override returns (uint8) {
    return 8;
}

import { parseEther, formatUnits } from "viem";
...
const myBalance = await tokenContract.read.balanceOf([deployer.account.address]);
console.log(`My Balance is ${formatUnits(myBalance, decimals)} ${symbol}`);
const otherBalance = await tokenContract.read.balanceOf([account1.account.address]);
console.log(
  `The Balance of Acc1 is ${formatUnits(otherBalance, decimals)} ${symbol}`
);

Events with solidity

• Event syntax
• Event storage
• Event indexing
• Topics and filters
• Transaction structure
• State changes with events

References

https://docs.soliditylang.org/en/latest/contracts.html#events

https://viem.sh/docs/glossary/terms#event-log

https://viem.sh/docs/actions/public/watchEvent.html

https://viem.sh/docs/contract/getContractEvents

Watching for events in tests

• Event syntax with Hardhat Chai Matchers
• Triggering an event
• Checking arguments

References

https://hardhat.org/hardhat-runner/docs/advanced/using-viem

https://hardhat.org/hardhat-runner/plugins/nomicfoundation-hardhat-viem

Code Reference

• Writing a test to trigger the Transfer event

import { expect } from "chai";
import { viem } from "hardhat";

describe("Basic tests for understanding ERC20", async () => {
  it("triggers the Transfer event with the address of the sender when sending transactions", async () => {
    const tokenContract = await viem.deployContract("MyToken");
    const publicClient = await viem.getPublicClient();
    const [deployer, account1] = await viem.getWalletClients();
    const hash = await tokenContract.write.transfer([account1.account.address, 1n]);
    await publicClient.waitForTransactionReceipt({ hash });
    const withdrawalEvents = await tokenContract.getEvents.Transfer();
    expect(withdrawalEvents).to.have.lengthOf(1);
    expect(withdrawalEvents[0].args.from?.toLowerCase()).to.equal(deployer.account.address);
    expect(withdrawalEvents[0].args.to?.toLowerCase()).to.equal(account1.account.address);
    expect(withdrawalEvents[0].args.value).to.equal(1n);
  });
});

Homework

• Create Github Issues with your questions about this lesson
• Read the references