Created
August 5, 2021 15:11
-
-
Save emilianobilli/175f14a59decdeee80e5ea57f2cb8ee4 to your computer and use it in GitHub Desktop.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
pragma solidity ^0.8.0; | |
/** | |
* @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.zeppelin.solutions/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}. | |
* | |
*/ | |
abstract contract Context { | |
function _msgSender() internal view returns (address) { | |
return msg.sender; | |
} | |
function _msgData() internal view returns (bytes calldata) { | |
return msg.data; | |
} | |
} | |
contract ERC20 is Context { | |
mapping(address => uint256) private _balances; | |
mapping(address => mapping(address => uint256)) private _allowances; | |
uint256 private _totalSupply; | |
string private _name; | |
string private _symbol; | |
/** | |
* @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 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 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. 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 returns (uint8) { | |
return 18; | |
} | |
/** | |
* @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(_msgSender(), 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 amount) public returns (bool) { | |
_approve(_msgSender(), 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}. | |
* | |
* Requirements: | |
* | |
* - `sender` and `recipient` cannot be the zero address. | |
* - `sender` must have a balance of at least `amount`. | |
* - 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); | |
uint256 currentAllowance = _allowances[sender][_msgSender()]; | |
require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance"); | |
unchecked { | |
_approve(sender, _msgSender(), currentAllowance - 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(_msgSender(), spender, _allowances[_msgSender()][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 returns (bool) { | |
uint256 currentAllowance = _allowances[_msgSender()][spender]; | |
require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero"); | |
unchecked { | |
_approve(_msgSender(), spender, currentAllowance - subtractedValue); | |
} | |
return true; | |
} | |
/** | |
* @dev Moves `amount` of tokens from `sender` to `recipient`. | |
* | |
* 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: | |
* | |
* - `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"); | |
_beforeTokenTransfer(sender, recipient, amount); | |
uint256 senderBalance = _balances[sender]; | |
require(senderBalance >= amount, "ERC20: transfer amount exceeds balance"); | |
unchecked { | |
_balances[sender] = senderBalance - amount; | |
} | |
_balances[recipient] += amount; | |
emit Transfer(sender, recipient, amount); | |
_afterTokenTransfer(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: | |
* | |
* - `account` cannot be the zero address. | |
*/ | |
function _mint(address account, uint256 amount) internal { | |
require(account != address(0), "ERC20: mint to the zero address"); | |
_beforeTokenTransfer(address(0), account, amount); | |
_totalSupply += amount; | |
_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 { | |
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; | |
} | |
_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 { | |
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 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 {} | |
/** | |
* @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 {} | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment