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ERC-20

导言

本教程帮助你创建一个符合Kaia 代币标准，尤其是Fungible Token Standard （ERC-20）的ERC-20 兼容代币示例。

ERC-20令牌标准定义了以下 2 个事件和 9 个方法（包括 3 个可选方法）。与 ERC-20 兼容的代币是实现以下接口的代币合约。


function name() public view returns (string) //optional
function symbol() public view returns (string) //optional
function decimals() public view returns (uint8) //optional
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)
event Transfer(address indexed _from, address indexed _to, uint256 _value)
event Approval(address indexed _owner, address indexed _spender, uint256 _value)

在上述界面的基础上，开发人员可以通过添加新功能和逻辑来定制令牌，并将其部署到 Kaia 网络上。更多信息，请参阅官方 ERC-20 文档。

在本教程中，您将实现与 ERC-20 兼容的令牌 MyERC20.sol。该代币将发行预定数量的代币，并在部署时将所有代币发送给合约所有者。

MyERC20.sol "基于 OpenZeppelin 的 ERC20 实现。本教程的大部分代码来自 OpenZeppelin 2.3 ，以下 Solidity 文件用于实现 MyERC20.sol。

1. 编写 ERC-20 智能合约

1.1 MyERC20 的总体结构

MyERC20.sol "的完整源代码如下。在此实现中，"构造器 "调用 "铸币"，在部署合约时铸入预定数量的代币。


pragma solidity ^0.5.0;
/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see `ERC20Detailed`.
 */
interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function transfer(address recipient, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
}
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");
        return c;
    }
    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a, "SafeMath: subtraction overflow");
        uint256 c = a - b;
        return c;
    }
    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
        if (a == 0) {
            return 0;
        }
        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;
    }
    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, "SafeMath: division by zero");
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold
        return c;
    }
    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b != 0, "SafeMath: modulo by zero");
        return a % b;
    }
}
/**
 * @dev Implementation of the `IERC20` interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using `_mint`.
 * For a generic mechanism see `ERC20Mintable`.
 *
 * *For a detailed writeup see our guide [How to implement supply
 * mechanisms](https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226).*
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an `Approval` event is emitted on calls to `transferFrom`.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard `decreaseAllowance` and `increaseAllowance`
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See `IERC20.approve`.
 */
contract MyERC20 is IERC20 {
    using SafeMath for uint256;
    mapping (address => uint256) private _balances;
    mapping (address => mapping (address => uint256)) private _allowances;
    // NOTE Start of https://github.com/OpenZeppelin/openzeppelin-solidity/blob/v2.3.0/contracts/token/ERC20/ERC20Detailed.sol
    string private _name;
    string private _symbol;
    uint8 private _decimals;
    constructor (string memory name, string memory symbol, uint8 decimals) public {
        _name = name;
        _symbol = symbol;
        _decimals = decimals;
        _mint(msg.sender, 100000 * 10 ** uint256(decimals)); // CAUTION!
    }
    /**
     * @dev Returns the name of the token.
     */
    function name() public view returns (string memory) {
        return _name;
    }
    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view returns (string memory) {
        return _symbol;
    }
    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei.
     *
     * > Note that this information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * `IERC20.balanceOf` and `IERC20.transfer`.
     */
    function decimals() public view returns (uint8) {
        return _decimals;
    }
    // NOTE End of https://github.com/OpenZeppelin/openzeppelin-solidity/blob/v2.3.0/contracts/token/ERC20/ERC20Detailed.sol
    uint256 private _totalSupply;
    /**
     * @dev See `IERC20.totalSupply`.
     */
    function totalSupply() public view returns (uint256) {
        return _totalSupply;
    }
    /**
     * @dev See `IERC20.balanceOf`.
     */
    function balanceOf(address account) public view returns (uint256) {
        return _balances[account];
    }
    /**
     * @dev See `IERC20.transfer`.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public returns (bool) {
        _transfer(msg.sender, recipient, amount);
        return true;
    }
    /**
     * @dev See `IERC20.allowance`.
     */
    function allowance(address owner, address spender) public view returns (uint256) {
        return _allowances[owner][spender];
    }
    /**
     * @dev See `IERC20.approve`.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 value) public returns (bool) {
        _approve(msg.sender, spender, value);
        return true;
    }
    /**
     * @dev See `IERC20.transferFrom`.
     *
     * Emits an `Approval` event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of `ERC20`;
     *
     * Requirements:
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `value`.
     * - the caller must have allowance for `sender`'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, msg.sender, _allowances[sender][msg.sender].sub(amount));
        return true;
    }
    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to `approve` that can be used as a mitigation for
     * problems described in `IERC20.approve`.
     *
     * Emits an `Approval` event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
        _approve(msg.sender, spender, _allowances[msg.sender][spender].add(addedValue));
        return true;
    }
    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to `approve` that can be used as a mitigation for
     * problems described in `IERC20.approve`.
     *
     * Emits an `Approval` event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
        _approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue));
        return true;
    }
    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to `transfer`, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a `Transfer` event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");
        _balances[sender] = _balances[sender].sub(amount);
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }
    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a `Transfer` event with `from` set to the zero address.
     *
     * Requirements
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal {
        require(account != address(0), "ERC20: mint to the zero address");
        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }
     /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a `Transfer` event with `to` set to the zero address.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 value) internal {
        require(account != address(0), "ERC20: burn from the zero address");
	_balances[account] = _balances[account].sub(value);
        _totalSupply = _totalSupply.sub(value);
        emit Transfer(account, address(0), value);
    }
    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens.
     *
     * This is internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an `Approval` event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 value) internal {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");
        _allowances[owner][spender] = value;
        emit Approval(owner, spender, value);
    }
    /**
     * @dev Destoys `amount` tokens from `account`.`amount` is then deducted
     * from the caller's allowance.
     *
     * See `_burn` and `_approve`.
     */
    function _burnFrom(address account, uint256 amount) internal {
        _burn(account, amount);
        _approve(account, msg.sender, _allowances[account][msg.sender].sub(amount));
    }
}

MyERC20.sol "由一个接口 "IERC20"、一个库 "SafeMath "和一个实现 "IERC20 "接口的合约 "MyERC20 "组成。

IERC20 "接口定义了ERC-20 规范中描述的强制接口。
SafeMath "库定义了 Solidity 算术运算的包装器，并增加了溢出检查功能，可安全计算 Solidity 的 "uint256 "类型。
MyERC20 "实现了 "IERC20 "接口，还定义了三个可选方法，详见ERC-20 规范。
- 除 ERC20 外，还定义了 "构造器"，该构造器用于定义新的 ERC20 令牌名称和符号，并铸造预定数量的令牌。 constructor 在首次部署时被调用一次。

1.2 看看重要的方法

让我们来详细了解一些重要的方法。

(1) `function balanceOf(address account) external view returns (uint256);`

balanceOf "是 ERC-20 的强制方法。 balanceOf 返回给定地址的余额。


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

balanceOf 只返回存储在 _balances中的 keyaccount 的值，它是 mapping (address => uint256)类型，如下所示。


    mapping (address => uint256) private _balances;

如果 _balances中没有可用的 key account ，则只会返回 0。

(2) `function transfer(address recipient, uint256 amount) external returns (bool);`

转让 "是 ERC-20 的强制性方法。 transfer "会将 "数量 "代币转移给 "接收方"，并且必须触发 "Transfer "事件。如果消息调用者的账户余额没有足够的代币可供使用，函数应抛出。

transfer "只是调用内部方法"_transfer"，它实现的实际传输和事件如下。


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

_transfer 实现 ERC-20 的 transfer 方法的实际行为。

此外，它还能防止使用下面的 require 从零地址或向零地址发送令牌。


    function _transfer(address sender, address recipient, uint256 amount) internal {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");
        _balances[sender] = _balances[sender].sub(amount);
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

(3) `function approve(address spender, uint256 amount) external returns (bool);`

批准 "是 ERC-20 的强制性方法。批准 "允许 "支出人 "多次从您的账户中提款，但以 "金额 "为限。如果多次调用此函数，则会将津贴重置为 amount。

approve "只是调用内部方法"_approve"，它实现了 "approve "的实际行为。 msg.sender "作为账户 "owner "传递。


    function approve(address spender, uint256 value) public returns (bool) {
        _approve(msg.sender, spender, value);
        return true;
    }
    function _approve(address owner, address spender, uint256 value) internal {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");
        _allowances[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

批准 "更新 "允许值"，"允许值 "是一个二维字典，保存了特定 "地址 "的 "支出人 "的允许 "值"。


    mapping (address => mapping (address => uint256)) private _allowances;

(4) `function _mint(address account, uint256 amount) internal`.

_mint 不是 ERC-20 的一部分。但是，我们需要一种方法来创建新的 ERC-20 令牌，因此在此实现中引入了 _mint 来创建新令牌，如下所示。


    function _mint(address account, uint256 amount) internal {
        require(account != address(0), "ERC20: mint to the zero address");
        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

_mint 是一个内部方法，可在本合同内部调用。

在MyERC20.sol中，当部署智能合约以铸造预定数量的代币时，_mint只从constructor调用一次。

如果想在部署智能合约后发行额外的代币，就必须引入一个新的公共方法，如 mint。实施该方法时应小心谨慎，因为只有授权用户才能铸造令牌。

更多详情，请参阅 OpenZeppelin 示例 ERC20Mintable.sol。

2. 部署智能合约

在本节中，您将使用 Remix Online IDE 部署 MyERC20 智能合约。 MYERC20.sol 的完整源代码见编写 ERC-20 智能合约。

2.1 先决条件

Kaia Wallet：用于部署合约、签署交易和与合约交互。
从水龙头测试 KAIA：为账户注入足够的 KAIA。

你可以使用 Remix Online IDE 或 Truffle 来部署 MyERC20 智能合约。

2.2 使用 Remix 在线集成开发环境部署智能合约

Remix IDE

导航至 Kaia Remix 插件
在合同文件夹中创建一个 MyERC20.sol 文件
在 Remix 中，点击编译合同。
安装插件后，点击左侧的 Kaia（前 Klaytn）选项卡
选择环境 > 注入式提供商 - Kaia Wallet。
在合同字段中，选择您的合同。例如，MyERC20。
在部署 KAIROSTOKEN、KAIROS 和 8 时分配以下参数
点击部署。

ERC20-1-deploy

部署完成后，可以使用用于部署合同的账户调用 balanceOf 。您会发现您的账户中有 10000000000000 代币，如下所示。由于您在部署上述合约时将 decimal 设置为 8，因此它在构造器中铸造了固定数量的 100000 代币，其中一个代币的十进制值为 10^8。 totalSupply "方法将返回已铸造代币的总供应量，也应为 "10000000000000"。

ERC20-2-owner-token

MyERC20 "现已上线！

3. 与 Kaia 钱包中的 ERC-20 令牌互动

您可以使用 Kaia 钱包查看余额，并转移您刚刚部署的与 ERC-20 兼容的 KAIROSTOKEN。要在 Kaia 钱包中查看令牌余额，请按以下步骤操作：

Kaia 钱包

打开 Kaia 钱包
点击令牌列表图标，然后点击添加令牌按钮

在 "自定义令牌 "选项卡下的 "令牌合约地址 "字段中粘贴 myERC20.sol 合约的地址。
然后按照提示添加令牌。您的令牌列表模式应该是这样的：

导言​

1. 编写 ERC-20 智能合约​

1.1 MyERC20 的总体结构​

1.2 看看重要的方法​

(1) function balanceOf(address account) external view returns (uint256);​

(2) function transfer(address recipient, uint256 amount) external returns (bool);​

(3) function approve(address spender, uint256 amount) external returns (bool);​

(4) function _mint(address account, uint256 amount) internal.​

2. 部署智能合约​

2.1 先决条件​

2.2 使用 Remix 在线集成开发环境部署智能合约​

3. 与 Kaia 钱包中的 ERC-20 令牌互动​

导言