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contracts/dependencies/openzeppelin/contracts/ERC20.sol
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// SPDX-License-Identifier: MIT | ||
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pragma solidity ^0.6.0; | ||
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import './Context.sol'; | ||
import './IERC20.sol'; | ||
import './SafeMath.sol'; | ||
import './Address.sol'; | ||
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/** | ||
* @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 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 ERC20 is Context, IERC20 { | ||
using SafeMath for uint256; | ||
using Address for address; | ||
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mapping(address => uint256) private _balances; | ||
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mapping(address => mapping(address => uint256)) private _allowances; | ||
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uint256 private _totalSupply; | ||
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string private _name; | ||
string private _symbol; | ||
uint8 private _decimals; | ||
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/** | ||
* @dev Sets the values for {name} and {symbol}, initializes {decimals} with | ||
* a default value of 18. | ||
* | ||
* To select a different value for {decimals}, use {_setupDecimals}. | ||
* | ||
* All three of these values are immutable: they can only be set once during | ||
* construction. | ||
*/ | ||
constructor(string memory name, string memory symbol) public { | ||
_name = name; | ||
_symbol = symbol; | ||
_decimals = 18; | ||
} | ||
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/** | ||
* @dev Returns the name of the token. | ||
*/ | ||
function name() public view returns (string memory) { | ||
return _name; | ||
} | ||
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/** | ||
* @dev Returns the symbol of the token, usually a shorter version of the | ||
* name. | ||
*/ | ||
function symbol() public view returns (string memory) { | ||
return _symbol; | ||
} | ||
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/** | ||
* @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 {_setupDecimals} is | ||
* called. | ||
* | ||
* 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 _decimals; | ||
} | ||
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/** | ||
* @dev See {IERC20-totalSupply}. | ||
*/ | ||
function totalSupply() public override view returns (uint256) { | ||
return _totalSupply; | ||
} | ||
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/** | ||
* @dev See {IERC20-balanceOf}. | ||
*/ | ||
function balanceOf(address account) public override view returns (uint256) { | ||
return _balances[account]; | ||
} | ||
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/** | ||
* @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 virtual override returns (bool) { | ||
_transfer(_msgSender(), recipient, amount); | ||
return true; | ||
} | ||
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/** | ||
* @dev See {IERC20-allowance}. | ||
*/ | ||
function allowance(address owner, address spender) | ||
public | ||
virtual | ||
override | ||
view | ||
returns (uint256) | ||
{ | ||
return _allowances[owner][spender]; | ||
} | ||
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/** | ||
* @dev See {IERC20-approve}. | ||
* | ||
* Requirements: | ||
* | ||
* - `spender` cannot be the zero address. | ||
*/ | ||
function approve(address spender, uint256 amount) public virtual override returns (bool) { | ||
_approve(_msgSender(), spender, amount); | ||
return true; | ||
} | ||
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/** | ||
* @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 virtual override returns (bool) { | ||
_transfer(sender, recipient, amount); | ||
_approve( | ||
sender, | ||
_msgSender(), | ||
_allowances[sender][_msgSender()].sub(amount, 'ERC20: transfer amount exceeds allowance') | ||
); | ||
return true; | ||
} | ||
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/** | ||
* @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) { | ||
_approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue)); | ||
return true; | ||
} | ||
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/** | ||
* @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) | ||
{ | ||
_approve( | ||
_msgSender(), | ||
spender, | ||
_allowances[_msgSender()][spender].sub( | ||
subtractedValue, | ||
'ERC20: decreased allowance below zero' | ||
) | ||
); | ||
return true; | ||
} | ||
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/** | ||
* @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 virtual { | ||
require(sender != address(0), 'ERC20: transfer from the zero address'); | ||
require(recipient != address(0), 'ERC20: transfer to the zero address'); | ||
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_beforeTokenTransfer(sender, recipient, amount); | ||
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_balances[sender] = _balances[sender].sub(amount, 'ERC20: transfer amount exceeds balance'); | ||
_balances[recipient] = _balances[recipient].add(amount); | ||
emit Transfer(sender, recipient, amount); | ||
} | ||
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/** @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 virtual { | ||
require(account != address(0), 'ERC20: mint to the zero address'); | ||
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_beforeTokenTransfer(address(0), account, amount); | ||
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_totalSupply = _totalSupply.add(amount); | ||
_balances[account] = _balances[account].add(amount); | ||
emit Transfer(address(0), account, amount); | ||
} | ||
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/** | ||
* @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'); | ||
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_beforeTokenTransfer(account, address(0), amount); | ||
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_balances[account] = _balances[account].sub(amount, 'ERC20: burn amount exceeds balance'); | ||
_totalSupply = _totalSupply.sub(amount); | ||
emit Transfer(account, address(0), amount); | ||
} | ||
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/** | ||
* @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 amount | ||
) internal virtual { | ||
require(owner != address(0), 'ERC20: approve from the zero address'); | ||
require(spender != address(0), 'ERC20: approve to the zero address'); | ||
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_allowances[owner][spender] = amount; | ||
emit Approval(owner, spender, amount); | ||
} | ||
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/** | ||
* @dev Sets {decimals} to a value other than the default one of 18. | ||
* | ||
* WARNING: This function should only be called from the constructor. Most | ||
* applications that interact with token contracts will not expect | ||
* {decimals} to ever change, and may work incorrectly if it does. | ||
*/ | ||
function _setupDecimals(uint8 decimals_) internal { | ||
_decimals = decimals_; | ||
} | ||
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/** | ||
* @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 to 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 {} | ||
} |
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