Contract Source Code:
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;
import {
ERC20,
IERC20
} from "@openzeppelin/[email protected]/token/ERC20/ERC20.sol";
import {Ownable} from "@openzeppelin/[email protected]/access/Ownable.sol";
/**
* Website: https://anonzk.io/
* VCC: https://vcc.anonzk.io/
* Twitter: https://twitter.com/AnonAZK
* Telegram: https://t.me/AnonZKPortal
* Docs: https://anonzk-documents.gitbook.io/anonzk/
*
* ▄████████ ███▄▄▄▄ ▄██████▄ ███▄▄▄▄ ▄███████▄ ▄█ ▄█▄
* ███ ███ ███▀▀▀██▄ ███ ███ ███▀▀▀██▄ ██▀ ▄██ ███ ▄███▀
* ███ ███ ███ ███ ███ ███ ███ ███ ▄███▀ ███▐██▀
* ███ ███ ███ ███ ███ ███ ███ ███ ▀█▀▄███▀▄▄ ▄█████▀
* ▀███████████ ███ ███ ███ ███ ███ ███ ▄███▀ ▀ ▀▀█████▄
* ███ ███ ███ ███ ███ ███ ███ ███ ▄███▀ ███▐██▄
* ███ ███ ███ ███ ███ ███ ███ ███ ███▄ ▄█ ███ ▀███▄
* ███ █▀ ▀█ █▀ ▀██████▀ ▀█ █▀ ▀████████▀ ███ ▀█▀
* ▀
*/
interface IUniswapV2Router02 {
function factory() external pure returns (address);
function WETH() external pure returns (address);
function swapExactTokensForETHSupportingFeeOnTransferTokens(
uint256 amountIn,
uint256 amountOutMin,
address[] calldata path,
address to,
uint256 deadline
) external;
function addLiquidityETH(
address token,
uint256 amountTokenDesired,
uint256 amountTokenMin,
uint256 amountETHMin,
address to,
uint256 deadline
) external payable returns (uint256 amountToken, uint256 amountETH, uint256 liquidity);
}
interface IUniswapV2Factory {
function createPair(address tokenA, address tokenB) external returns (address pair);
}
contract AnonZK is ERC20, Ownable {
// errors
error ErrAlreadySetup();
error ErrAlreadyLaunched();
error ErrMaxBalance();
error ErrMaxTx();
error ErrInvalidFees();
error ErrInvalidSwapThreshold();
error ErrAddressZero();
error ErrZeroValue();
error ErrZeroToken();
error ErrTradingNotStarted();
// states
address constant FEE_RECEIVER = 0xC8aFc08747213Da2Ab68373E5B261dd304390270;
uint256 public constant MAX_SUPPLY = 10 * 1e6 ether;
IUniswapV2Router02 public constant UNISWAP_V2_ROUTER =
IUniswapV2Router02(0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D);
uint256 private constant INITIAL_MAX_TRANSACTION_AMOUNT = 3 * 1e5 ether; // 3% from total supply maxTransactionAmountTxn
uint256 private constant INITIAL_MAX_WALLET = 3 * 1e5 ether; // 3% from total supply maxWallet
uint256 private constant INITIAL_BUY_FEE = 5;
uint256 private constant INITIAL_SELL_FEE = 30;
address public uniswapPair;
mapping(address => bool) private _limitExempted;
mapping(address => bool) private _feeExempted;
uint256 public maxWallet;
uint256 public maxTx;
address public feeReceiver;
uint256 public buyFee;
uint256 public sellFee;
uint256 private _swapThreshold;
bool private _isSwapping;
bool public tradingStarted;
constructor() ERC20("AnonZK", unicode"AZK") {
// set states
_limitExempted[tx.origin] = true;
_limitExempted[address(0)] = true;
_limitExempted[address(0xdead)] = true;
_limitExempted[address(this)] = true;
_limitExempted[address(UNISWAP_V2_ROUTER)] = true;
_feeExempted[address(this)] = true;
_feeExempted[tx.origin] = true;
maxWallet = INITIAL_MAX_WALLET;
maxTx = INITIAL_MAX_TRANSACTION_AMOUNT;
buyFee = INITIAL_BUY_FEE;
sellFee = INITIAL_SELL_FEE;
feeReceiver = FEE_RECEIVER;
_swapThreshold = MAX_SUPPLY / 100;
// mint
_mint(tx.origin, MAX_SUPPLY);
}
receive() external payable {}
fallback() external payable {}
// erc20
function _beforeTokenTransfer(address from_, address to_, uint256 amount_) internal view override {
// check limits max wallet
if (!_limitExempted[to_]) {
if (balanceOf(to_) + amount_ > maxWallet) {
revert ErrMaxBalance();
}
}
// check max tx
if (!_limitExempted[from_]) {
if (amount_ > maxTx) {
revert ErrMaxTx();
}
}
// check trading started
if (!tradingStarted) {
if (!_feeExempted[from_] && !_feeExempted[to_]) {
revert ErrTradingNotStarted();
}
}
}
function _transfer(address from_, address to_, uint256 amount_) internal override {
// check
if (to_ == address(0)) revert ErrAddressZero();
// zero amount
if (amount_ == 0) {
super._transfer(from_, to_, 0);
return;
}
// swap
if (
!_isSwapping && balanceOf(address(this)) >= _swapThreshold && from_ != uniswapPair && !_feeExempted[from_]
&& !_feeExempted[to_]
) {
_isSwapping = true;
_swap();
_isSwapping = false;
}
// fees
uint256 fees = 0;
if (!_isSwapping && !_feeExempted[from_] && !_feeExempted[to_]) {
uint256 _sellTax = sellFee;
uint256 _buyTax = buyFee;
// on sell
if (to_ == uniswapPair && _sellTax > 0) {
fees = (amount_ * _sellTax) / 100;
super._transfer(from_, address(this), fees);
}
// on buy
else if (from_ == uniswapPair && _buyTax > 0) {
fees = (amount_ * _buyTax) / 100;
super._transfer(from_, address(this), fees);
}
}
super._transfer(from_, to_, amount_ - fees);
}
// owners
function launch(uint256 tokenAmount_) external payable onlyOwner {
// check if already launched
if (uniswapPair != address(0)) revert ErrAlreadyLaunched();
// check token & value
if (msg.value == 0) revert ErrZeroValue();
if (tokenAmount_ == 0) revert ErrZeroToken();
// transfer token
_transfer(msg.sender, address(this), tokenAmount_);
// create pair
IUniswapV2Router02 __router = UNISWAP_V2_ROUTER;
address __uniswapPair = IUniswapV2Factory(__router.factory()).createPair(address(this), __router.WETH());
// update state
_limitExempted[__uniswapPair] = true;
// approve tokens
_approve(address(this), address(__router), type(uint256).max);
_approve(address(this), address(__uniswapPair), type(uint256).max);
IERC20(__uniswapPair).approve(address(__router), type(uint256).max);
// add liq
__router.addLiquidityETH{value: address(this).balance}(
address(this), balanceOf(address(this)), 0, 0, owner(), block.timestamp
);
uniswapPair = __uniswapPair;
}
function clearStuck() external onlyOwner {
(bool success,) = payable(msg.sender).call{value: address(this).balance}("");
require(success);
}
function clearStuckToken() external onlyOwner {
_transfer(address(this), msg.sender, balanceOf(address(this)));
}
function setLimitExempted(address addr_, bool exempted_) external onlyOwner {
_limitExempted[addr_] = exempted_;
}
function setFeeExempted(address addr_, bool exempted_) external onlyOwner {
_feeExempted[addr_] = exempted_;
}
function setMaxWallet(uint256 maxWallet_) external onlyOwner {
maxWallet = maxWallet_;
}
function setMaxTx(uint256 maxTx_) external onlyOwner {
maxTx = maxTx_;
}
function setFeeReceiver(address addr_) external onlyOwner {
feeReceiver = addr_;
}
function setFees(uint256 buyFee_, uint256 sellFee_) external onlyOwner {
if (buyFee_ > 100 || sellFee_ > 100) {
revert ErrInvalidFees();
}
sellFee = sellFee_;
buyFee = buyFee_;
}
function setSwapThreshold(uint256 swapThreshold_) external onlyOwner {
uint256 __totalSupply = MAX_SUPPLY;
if (swapThreshold_ < __totalSupply / 1000 || swapThreshold_ > __totalSupply / 20) {
revert ErrInvalidSwapThreshold();
}
_swapThreshold = swapThreshold_;
}
function enableTrading() external onlyOwner {
tradingStarted = true;
}
// internal
function _swapTokensForEth(uint256 tokenAmount) private {
IUniswapV2Router02 __swapRouter = UNISWAP_V2_ROUTER;
// generate the uniswap pair path of token -> weth
address[] memory path = new address[](2);
path[0] = address(this);
path[1] = __swapRouter.WETH();
_approve(address(this), address(__swapRouter), tokenAmount);
// make the swap
__swapRouter.swapExactTokensForETHSupportingFeeOnTransferTokens(
tokenAmount, 0, path, address(this), block.timestamp
);
}
function _swap() private {
uint256 __contractBalance = balanceOf(address(this));
uint256 __swapThreshold = _swapThreshold;
// nothing to swap
if (__contractBalance == 0) {
return;
}
// swap amount
uint256 __swapAmount = __contractBalance;
if (__swapAmount > __swapThreshold * 20) {
__swapAmount = __swapThreshold * 20;
}
// swap to ETH
_swapTokensForEth(__swapAmount);
// send
uint256 __balance = address(this).balance;
(bool success,) = payable(address(feeReceiver)).call{value: __balance}("");
}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (access/Ownable.sol)
pragma solidity ^0.8.0;
import "../utils/Context.sol";
/**
* @dev Contract module which provides a basic access control mechanism, where
* there is an account (an owner) that can be granted exclusive access to
* specific functions.
*
* By default, the owner account will be the one that deploys the contract. This
* can later be changed with {transferOwnership}.
*
* This module is used through inheritance. It will make available the modifier
* `onlyOwner`, which can be applied to your functions to restrict their use to
* the owner.
*/
abstract contract Ownable is Context {
address private _owner;
event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
/**
* @dev Initializes the contract setting the deployer as the initial owner.
*/
constructor() {
_transferOwnership(_msgSender());
}
/**
* @dev Throws if called by any account other than the owner.
*/
modifier onlyOwner() {
_checkOwner();
_;
}
/**
* @dev Returns the address of the current owner.
*/
function owner() public view virtual returns (address) {
return _owner;
}
/**
* @dev Throws if the sender is not the owner.
*/
function _checkOwner() internal view virtual {
require(owner() == _msgSender(), "Ownable: caller is not the owner");
}
/**
* @dev Leaves the contract without owner. It will not be possible to call
* `onlyOwner` functions anymore. Can only be called by the current owner.
*
* NOTE: Renouncing ownership will leave the contract without an owner,
* thereby removing any functionality that is only available to the owner.
*/
function renounceOwnership() public virtual onlyOwner {
_transferOwnership(address(0));
}
/**
* @dev Transfers ownership of the contract to a new account (`newOwner`).
* Can only be called by the current owner.
*/
function transferOwnership(address newOwner) public virtual onlyOwner {
require(newOwner != address(0), "Ownable: new owner is the zero address");
_transferOwnership(newOwner);
}
/**
* @dev Transfers ownership of the contract to a new account (`newOwner`).
* Internal function without access restriction.
*/
function _transferOwnership(address newOwner) internal virtual {
address oldOwner = _owner;
_owner = newOwner;
emit OwnershipTransferred(oldOwner, newOwner);
}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.8.0) (token/ERC20/ERC20.sol)
pragma solidity ^0.8.0;
import "./IERC20.sol";
import "./extensions/IERC20Metadata.sol";
import "../../utils/Context.sol";
/**
* @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 {ERC20PresetMinterPauser}.
*
* TIP: For a detailed writeup see our guide
* https://forum.openzeppelin.com/t/how-to-implement-erc20-supply-mechanisms/226[How
* to implement supply mechanisms].
*
* We have followed general OpenZeppelin Contracts guidelines: functions revert
* instead 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 ERC20 is Context, IERC20, IERC20Metadata {
mapping(address => uint256) private _balances;
mapping(address => mapping(address => uint256)) private _allowances;
uint256 private _totalSupply;
string private _name;
string private _symbol;
/**
* @dev Sets the values for {name} and {symbol}.
*
* The default value of {decimals} is 18. To select a different value for
* {decimals} you should overload it.
*
* All two of these values are immutable: they can only be set once during
* construction.
*/
constructor(string memory name_, string memory symbol_) {
_name = name_;
_symbol = symbol_;
}
/**
* @dev Returns the name of the token.
*/
function name() public view virtual override returns (string memory) {
return _name;
}
/**
* @dev Returns the symbol of the token, usually a shorter version of the
* name.
*/
function symbol() public view virtual override 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. This is the value {ERC20} uses, unless this function is
* overridden;
*
* NOTE: 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 virtual override returns (uint8) {
return 18;
}
/**
* @dev See {IERC20-totalSupply}.
*/
function totalSupply() public view virtual override returns (uint256) {
return _totalSupply;
}
/**
* @dev See {IERC20-balanceOf}.
*/
function balanceOf(address account) public view virtual override returns (uint256) {
return _balances[account];
}
/**
* @dev See {IERC20-transfer}.
*
* Requirements:
*
* - `to` cannot be the zero address.
* - the caller must have a balance of at least `amount`.
*/
function transfer(address to, uint256 amount) public virtual override returns (bool) {
address owner = _msgSender();
_transfer(owner, to, amount);
return true;
}
/**
* @dev See {IERC20-allowance}.
*/
function allowance(address owner, address spender) public view virtual override returns (uint256) {
return _allowances[owner][spender];
}
/**
* @dev See {IERC20-approve}.
*
* NOTE: If `amount` is the maximum `uint256`, the allowance is not updated on
* `transferFrom`. This is semantically equivalent to an infinite approval.
*
* Requirements:
*
* - `spender` cannot be the zero address.
*/
function approve(address spender, uint256 amount) public virtual override returns (bool) {
address owner = _msgSender();
_approve(owner, spender, amount);
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}.
*
* NOTE: Does not update the allowance if the current allowance
* is the maximum `uint256`.
*
* Requirements:
*
* - `from` and `to` cannot be the zero address.
* - `from` must have a balance of at least `amount`.
* - the caller must have allowance for ``from``'s tokens of at least
* `amount`.
*/
function transferFrom(
address from,
address to,
uint256 amount
) public virtual override returns (bool) {
address spender = _msgSender();
_spendAllowance(from, spender, amount);
_transfer(from, to, 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 virtual returns (bool) {
address owner = _msgSender();
_approve(owner, spender, allowance(owner, spender) + 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 virtual returns (bool) {
address owner = _msgSender();
uint256 currentAllowance = allowance(owner, spender);
require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
unchecked {
_approve(owner, spender, currentAllowance - subtractedValue);
}
return true;
}
/**
* @dev Moves `amount` of tokens from `from` to `to`.
*
* This 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:
*
* - `from` cannot be the zero address.
* - `to` cannot be the zero address.
* - `from` must have a balance of at least `amount`.
*/
function _transfer(
address from,
address to,
uint256 amount
) internal virtual {
require(from != address(0), "ERC20: transfer from the zero address");
require(to != address(0), "ERC20: transfer to the zero address");
_beforeTokenTransfer(from, to, amount);
uint256 fromBalance = _balances[from];
require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
unchecked {
_balances[from] = fromBalance - amount;
// Overflow not possible: the sum of all balances is capped by totalSupply, and the sum is preserved by
// decrementing then incrementing.
_balances[to] += amount;
}
emit Transfer(from, to, amount);
_afterTokenTransfer(from, to, 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:
*
* - `account` cannot be the zero address.
*/
function _mint(address account, uint256 amount) internal virtual {
require(account != address(0), "ERC20: mint to the zero address");
_beforeTokenTransfer(address(0), account, amount);
_totalSupply += amount;
unchecked {
// Overflow not possible: balance + amount is at most totalSupply + amount, which is checked above.
_balances[account] += amount;
}
emit Transfer(address(0), account, amount);
_afterTokenTransfer(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 amount) internal virtual {
require(account != address(0), "ERC20: burn from the zero address");
_beforeTokenTransfer(account, address(0), amount);
uint256 accountBalance = _balances[account];
require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
unchecked {
_balances[account] = accountBalance - amount;
// Overflow not possible: amount <= accountBalance <= totalSupply.
_totalSupply -= amount;
}
emit Transfer(account, address(0), amount);
_afterTokenTransfer(account, address(0), amount);
}
/**
* @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
*
* This 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 amount
) internal virtual {
require(owner != address(0), "ERC20: approve from the zero address");
require(spender != address(0), "ERC20: approve to the zero address");
_allowances[owner][spender] = amount;
emit Approval(owner, spender, amount);
}
/**
* @dev Updates `owner` s allowance for `spender` based on spent `amount`.
*
* Does not update the allowance amount in case of infinite allowance.
* Revert if not enough allowance is available.
*
* Might emit an {Approval} event.
*/
function _spendAllowance(
address owner,
address spender,
uint256 amount
) internal virtual {
uint256 currentAllowance = allowance(owner, spender);
if (currentAllowance != type(uint256).max) {
require(currentAllowance >= amount, "ERC20: insufficient allowance");
unchecked {
_approve(owner, spender, currentAllowance - amount);
}
}
}
/**
* @dev Hook that is called before any transfer of tokens. This includes
* minting and burning.
*
* Calling conditions:
*
* - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
* will be transferred to `to`.
* - when `from` is zero, `amount` tokens will be minted for `to`.
* - when `to` is zero, `amount` of ``from``'s tokens will be burned.
* - `from` and `to` are never both zero.
*
* To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
*/
function _beforeTokenTransfer(
address from,
address to,
uint256 amount
) internal virtual {}
/**
* @dev Hook that is called after any transfer of tokens. This includes
* minting and burning.
*
* Calling conditions:
*
* - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
* has been transferred to `to`.
* - when `from` is zero, `amount` tokens have been minted for `to`.
* - when `to` is zero, `amount` of ``from``'s tokens have been burned.
* - `from` and `to` are never both zero.
*
* To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
*/
function _afterTokenTransfer(
address from,
address to,
uint256 amount
) internal virtual {}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)
pragma solidity ^0.8.0;
/**
* @dev Provides information about the current execution context, including the
* sender of the transaction and its data. While these are generally available
* via msg.sender and msg.data, they should not be accessed in such a direct
* manner, since when dealing with meta-transactions the account sending and
* paying for execution may not be the actual sender (as far as an application
* is concerned).
*
* This contract is only required for intermediate, library-like contracts.
*/
abstract contract Context {
function _msgSender() internal view virtual returns (address) {
return msg.sender;
}
function _msgData() internal view virtual returns (bytes calldata) {
return msg.data;
}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)
pragma solidity ^0.8.0;
import "../IERC20.sol";
/**
* @dev Interface for the optional metadata functions from the ERC20 standard.
*
* _Available since v4.1._
*/
interface IERC20Metadata is IERC20 {
/**
* @dev Returns the name of the token.
*/
function name() external view returns (string memory);
/**
* @dev Returns the symbol of the token.
*/
function symbol() external view returns (string memory);
/**
* @dev Returns the decimals places of the token.
*/
function decimals() external view returns (uint8);
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC20/IERC20.sol)
pragma solidity ^0.8.0;
/**
* @dev Interface of the ERC20 standard as defined in the EIP.
*/
interface IERC20 {
/**
* @dev Emitted when `value` tokens are moved from one account (`from`) to
* another (`to`).
*
* Note that `value` may be zero.
*/
event Transfer(address indexed from, address indexed to, uint256 value);
/**
* @dev Emitted when the allowance of a `spender` for an `owner` is set by
* a call to {approve}. `value` is the new allowance.
*/
event Approval(address indexed owner, address indexed spender, uint256 value);
/**
* @dev Returns the amount of tokens in existence.
*/
function totalSupply() external view returns (uint256);
/**
* @dev Returns the amount of tokens owned by `account`.
*/
function balanceOf(address account) external view returns (uint256);
/**
* @dev Moves `amount` tokens from the caller's account to `to`.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* Emits a {Transfer} event.
*/
function transfer(address to, uint256 amount) external returns (bool);
/**
* @dev Returns the remaining number of tokens that `spender` will be
* allowed to spend on behalf of `owner` through {transferFrom}. This is
* zero by default.
*
* This value changes when {approve} or {transferFrom} are called.
*/
function allowance(address owner, address spender) external view returns (uint256);
/**
* @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* IMPORTANT: Beware that changing an allowance with this method brings the risk
* that someone may use both the old and the new allowance by unfortunate
* transaction ordering. One possible solution to mitigate this race
* condition is to first reduce the spender's allowance to 0 and set the
* desired value afterwards:
* https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
*
* Emits an {Approval} event.
*/
function approve(address spender, uint256 amount) external returns (bool);
/**
* @dev Moves `amount` tokens from `from` to `to` using the
* allowance mechanism. `amount` is then deducted from the caller's
* allowance.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* Emits a {Transfer} event.
*/
function transferFrom(
address from,
address to,
uint256 amount
) external returns (bool);
}