## Moccasin ERC20 Introduction We are about to learn a ton about ERC20 tokens, and how to deploy them. We'll also see a bug that we'll intentionally create in our smart contract. ### Project Walkthrough Let's first take a look at the project. We're working with a GitHub repo that has an ERC20 project. We'll see that this project has a few things, including a contracts folder, a tests folder, and a script folder. We will also be creating our own custom token. We'll start with a base ERC20 token and then customize it to our liking. ### Snekmate We're going to use a library called Snekmate to help us build our custom token. Snekmate is a Vyper library that provides a ton of boilerplate code for common smart contract functionality. ### Custom ERC20 We will create a custom token that includes: - `name` - `symbol` - `decimals` - `eip712 version` ### Deploying the Token To deploy our token, we will use the `moxc` tool. ```bash moxc run deploy ``` ### Events We will also learn about events. Events are a way for smart contracts to communicate with the outside world. ### Testing We will use a combination of unit tests and fuzz tests to ensure our ERC20 token is secure and functional. - **Fuzz Testing** - Fuzz tests are a type of testing that involves generating random inputs and then running them against your smart contract. Fuzz testing is particularly useful for finding security vulnerabilities. - **Stateless and Stateful Fuzzing** - We will learn how to create both stateless and stateful fuzzers. ### Formatting We will also learn how to format our smart contract code in a way that automatically ensures our code is consistent and professional. ### Code Blocks ```python pragma version ^0.4.1 ``` ```python license MIT ``` ```python title snek_token ``` ```python author You! ``` ```python notice This is my ERC20 token! ``` ```python from ethereum.ercs import ERC20 ``` ```python implements: ERC20 ``` ```python from ethereum.ercs import ERC20Detailed ``` ```python implements: ERC20Detailed ``` ```python from snekmate.auth import ownable as ow ``` ```python initializes: ow ``` ```python from snekmate.tokens import erc20 ``` ```python initializes: erc20(ownable = ow) ``` ```python exports: erc20._interface_ ``` ```python NAME: constant(String[25]) = "snek token" ``` ```python SYMBOL: constant(String[5]) = "SNEK" ``` ```python DECIMALS: constant(uint8) = 18 ``` ```python EIP712_VERSION: constant(String[20]) = "1" ``` ```python initialSupply: uint256 ``` ```python @deploy def __init__(initial_supply: uint256): ow.__init__() erc20.__init__(NAME, SYMBOL, DECIMALS, NAME, EIP712_VERSION) erc20.mint(msg.sender, initial_supply) self.initialSupply = erc20.totalSupply ``` ```python @external def super_mint(): # We forget to update the total supply! amount: uint256 = as_wei_value(100, "ether") self.totalSupply += amount erc20.balanceOf(msg.sender) = erc20.balanceOf(msg.sender) + amount log ERC20.Transfer(empty_address, msg.sender, amount) ``` ```python from script.deploy import deploy ``` ```python from eth_utils import to_wei ``` ```python from moccasin.boa_tools import VyperContract ``` ```python from contracts import snek_token ``` ```python INITIAL_SUPPLY = to_wei(1000, "ether") ``` ```python def deploy() -> VyperContract: snek_contract = snek_token.deploy(INITIAL_SUPPLY) print(f"Deployed SnekToken at {snek_contract.address}") return snek_contract ``` ```python def moccasine_main() -> VyperContract: return deploy() ``` This is just a brief introduction to ERC20 tokens and how to deploy them. This lesson will help you get started with this kind of smart contract.