#鐵人賽 #ethereum #solidity

今天開始來補完全部 ERC20 的功能吧！
本日實作的函式：

1. name()
2. symbol()
3. decimals()
4. mint()
5. burn()

本日影片： https://youtu.be/kbYrFXvfgno
本日合約：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;

interface IERC20 {
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    function totalSupply() external view returns (uint256);

    function balanceOf(address account) external view returns (uint256);
    function allowance(address owner, address spender) external view returns (uint256);
    
    function approve(address spender, uint256 amount) external returns (bool);
    function transfer(address to, uint256 amount) external returns (bool);
    function transferFrom(address from, address to, uint256 amount) external returns (bool);
}

contract ERC20 is IERC20 {
    uint256 _totalSupply;
    mapping(address => uint256) _balance;
    mapping(address => mapping(address => uint256)) _allowance;
    string _name;
    string _symbol;
    address _owner;

    modifier onlyOwner() {
        require(_owner == msg.sender, "ERROR: only owner can access this function");
        _;
    }

    constructor(string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
        _owner = msg.sender;

        _balance[msg.sender] = 10000;
        _totalSupply = 10000;
    }

    function mint(address account, uint256 amount) public onlyOwner {
        require(account != address(0), "ERROR: mint to address 0");
        _totalSupply += amount;
        _balance[account] += amount;
        emit Transfer(address(0), account, amount);
    }

    function burn(address account, uint256 amount) public onlyOwner {
        require(account != address(0), "ERROR: burn from address 0");
        uint256 accountBalance = _balance[account];
        require(accountBalance >= amount, "ERROR: no more token to burn");
        _balance[account] = accountBalance - amount;
        _totalSupply -= amount;
        emit Transfer(account, address(0), amount);
    }

    function name() public view returns (string memory) {
        return _name;
    }
    function symbol() public view returns (string memory) {
        return _symbol;
    }
    function decimals() public pure returns (uint8) {
        return 18;
    }

    function totalSupply() public view returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) public view returns (uint256) {
        return _balance[account];
    }

    function _transfer(address from, address to, uint256 amount) internal {
        uint256 myBalance = _balance[from];
        require(myBalance >= amount, "No money to transfer");
        require(to != address(0), "Transfer to address 0");

        _balance[from] = myBalance - amount;
        _balance[to] = _balance[to] + amount;
        emit Transfer(from, to, amount);
    }

    function transfer(address to, uint256 amount) public returns (bool) {
        _transfer(msg.sender, to, amount);
        return true;
    }

    function allowance(address owner, address spender) public view returns (uint256) {
        return _allowance[owner][spender];
    }

    function _approve(address owner, address spender, uint256 amount) internal {
        _allowance[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }
    
    function approve(address spender, uint256 amount) public returns (bool) {
        _approve(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(address from, address to, uint256 amount) public returns (bool) {
        uint256 myAllowance = _allowance[from][msg.sender];
        require(myAllowance >= amount, "ERROR: myAllowance < amount");

        _approve(from, msg.sender, myAllowance - amount);
        _transfer(from, to, amount);
        return true;
    }
}

本影片提到的連結：
「Remix IDE」： https://remix.ethereum.org/
「在 2022 年，我們該如何寫智能合約」： https://ithelp.ithome.com.tw/users/20083367/ironman/5019
「那些關於 Ethereum 的事」： https://ithelp.ithome.com.tw/users/20083367/ironman/5136
「一本關於 Ethereum 與 Solidity 智能合約的書」： https://solidity.tw
「文章或主題許願池」： https://github.com/hydai/solidity-book/issues
「本系列播放清單」： https://www.youtube.com/playlist?list=PLHmOMPRfmOxQYDnXAc1hKY6ra4WDU8ZlM