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December 22, 2019 15:28
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pragma solidity ^0.5.0; | |
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/GSN/Context.sol"; | |
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/IERC20.sol"; | |
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/SafeMath.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 {ERC20Mintable}. | |
* | |
* 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; | |
string private _name; | |
string private _symbol; | |
uint8 private _decimals; | |
/** | |
* @dev Sets the values for `name`, `symbol`, and `decimals`. All three of | |
* these values are immutable: they can only be set once during | |
* construction. | |
*/ | |
constructor () public { | |
_name = 'Test Tokens'; | |
_symbol = 'TEST'; | |
_decimals = 18; | |
} | |
/** | |
* @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: 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; | |
} | |
mapping (address => uint256) private _balances; | |
mapping (address => mapping (address => uint256)) private _allowances; | |
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(_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); | |
_approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance")); | |
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].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(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero")); | |
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, "ERC20: transfer amount exceeds balance"); | |
_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) public { | |
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 amount) internal { | |
require(account != address(0), "ERC20: burn from the zero address"); | |
_balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance"); | |
_totalSupply = _totalSupply.sub(amount); | |
emit Transfer(account, address(0), amount); | |
} | |
/** | |
* @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 { | |
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 Destroys `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, _msgSender(), _allowances[account][_msgSender()].sub(amount, "ERC20: burn amount exceeds allowance")); | |
} | |
} |
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