第1节：ERC20（标准Token）

1. EIP: Ethereum Improvement Propose
2. 任何遵从EIP-20协议（ERC20标准）的Contract都属于ERC20 Token

标准接口

// 6 REQUIRED FUNCTIONS
function totalSupply() public view returns (uint256)
function balanceOf(address _owner) public view returns (uint256 balance)
function transfer(address _to, uint256 _value) public returns (bool success)
function transferFrom(address _from, address _to, uint256 _value) public returns (bool success)
function approve(address _spender, uint256 _value) public returns (bool success)
function allowance(address _owner, address _spender) public view returns (uint256 remaining)

// 2 REQUIRED EVENTS
event Transfer(address indexed _from, address indexed _to, uint256 _value)
event Approval(address indexed _owner, address indexed _spender, uint256 _value)

// 3. OPTIONAL FUNCTIONS
function name() public view returns (string)
function symbol() public view returns (string)
function decimals() public view returns (uint8)

分析

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.13;

// https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v3.0.0/contracts/token/ERC20/IERC20.sol
interface IERC20 {
      // 6 REQUIRED FUNCTIONS
      // 总发行量
    function totalSupply() external view returns (uint);  // -> 总发行量 100000000 * 10**decimals

      // 标准decimal： 18
      // USDT: 6
      // WBTC: 8
    function balanceOf(address account) external view returns (uint); // 指定账户的余额

    // 币的持有人直接调用，进行转账
    function transfer(address recipient, uint amount) external returns (bool);

      // 最常用的！！
      // 1. 我这个owner对合约进行approve，此时approve内部会修改allowance变量
      // 2. 合约内部调用transferFrom来支配owner的token
    function transferFrom( // spender就是这个合约
        address sender,    // owner
        address recipient,    // 转给谁
        uint amount // 金额
    ) external returns (bool);


    // owner: 币的持有人
      // spender: 是指定帮助花费的代理人（被授权的人）
    function allowance(address owner, address spender) external view returns (uint); // 授权的额度

    // decimals view，这是一个public 的变量，自动提供了一个读取的方法 // 返回精度
      // 持有人对spender进行授权，在approve内部，会调用msg.sender来知道owner是谁
    function approve(address spender, uint amount) external returns (bool);

      // 2 REQUIRED EVENTS
      // 事件
    event Transfer(address indexed from, address indexed to, uint value);
    event Approval(address indexed owner, address indexed spender, uint value);

    // 3. OPTIONAL FUNCTIONS
    function name() public view returns (string)
    function symbol() public view returns (string)
    function decimals() public view returns (uint8)
}

以下是ERC20的案例：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.13;

import "./IERC20.sol";

contract ERC20 is IERC20 {
    uint public totalSupply;
    mapping(address => uint) public balanceOf;
    mapping(address => mapping(address => uint)) public allowance;
    string public name = "Solidity by Example";
    string public symbol = "SOLBYEX";
    uint8 public decimals = 18;

    function transfer(address recipient, uint amount) external returns (bool) {
        balanceOf[msg.sender] -= amount;
        balanceOf[recipient] += amount;
        emit Transfer(msg.sender, recipient, amount);
        return true;
    }

    function approve(address spender, uint amount) external returns (bool) {
        allowance[msg.sender][spender] = amount;
        emit Approval(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(
        address sender,
        address recipient,
        uint amount
    ) external returns (bool) {
        allowance[sender][msg.sender] -= amount;
        balanceOf[sender] -= amount;
        balanceOf[recipient] += amount;
        emit Transfer(sender, recipient, amount);
        return true;
    }

    function mint(uint amount) external {
        balanceOf[msg.sender] += amount;
        totalSupply += amount;
        emit Transfer(address(0), msg.sender, amount);
    }

    function burn(uint amount) external {
        balanceOf[msg.sender] -= amount;
        totalSupply -= amount;
        emit Transfer(msg.sender, address(0), amount);
    }
}

可以使用openzeppelin库进行创建自己的token：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.13;

// import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.0.0/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";


contract MyToken is ERC20 {
    constructor(string memory name, string memory symbol) ERC20(name, symbol) {
        // Mint 100 tokens to msg.sender
        // Similar to how
        // 1 dollar = 100 cents
        // 1 token = 1 * (10 ** decimals)
        _mint(msg.sender, 100 * 10**uint(decimals()));
    }

    // 默认是18，可以进行override
    function decimals() public view override returns (uint8) {
        return 6;
    }
}