206 lines
7.9 KiB
Solidity
206 lines
7.9 KiB
Solidity
pragma solidity ^0.5.0;
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import "./IERC20.sol";
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import "../../math/SafeMath.sol";
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/**
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* @dev Implementation of the `IERC20` interface.
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*
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* This implementation is agnostic to the way tokens are created. This means
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* that a supply mechanism has to be added in a derived contract using `_mint`.
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* For a generic mechanism see `ERC20Mintable`.
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*
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* *For a detailed writeup see our guide [How to implement supply
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* mechanisms](https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226).*
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*
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* We have followed general OpenZeppelin guidelines: functions revert instead
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* of returning `false` on failure. This behavior is nonetheless conventional
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* and does not conflict with the expectations of ERC20 applications.
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*
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* Additionally, an `Approval` event is emitted on calls to `transferFrom`.
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* This allows applications to reconstruct the allowance for all accounts just
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* by listening to said events. Other implementations of the EIP may not emit
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* these events, as it isn't required by the specification.
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*
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* Finally, the non-standard `decreaseAllowance` and `increaseAllowance`
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* functions have been added to mitigate the well-known issues around setting
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* allowances. See `IERC20.approve`.
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*/
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contract ERC20 is IERC20 {
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using SafeMath for uint256;
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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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/**
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* @dev Returns the amount of tokens owned by an account (`owner`). See `IERC20.balanceOf`.
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*/
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function balanceOf(address owner) public view returns (uint256) {
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return _balances[owner];
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}
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/**
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* @dev Moves tokens from the caller's account to a specified recipient
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* (`to`). See `IERC20.transfer`.
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*
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* Requirements
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*
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* - `to` cannot be the zero address.
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*/
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function transfer(address to, uint256 value) public returns (bool) {
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_transfer(msg.sender, to, value);
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return true;
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}
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/**
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* @dev Configures the amount that a `spender` account is able to spend on
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* behalf of the caller. See `IERC20.approve`.
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*
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* > `approve` can be abused by an untrusted spender.
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*
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* Requirements
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*
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* - `spender` cannot be the zero address.
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*/
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function approve(address spender, uint256 value) public returns (bool) {
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_approve(msg.sender, spender, value);
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return true;
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}
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/**
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* @dev Function to check the amount of tokens that an owner allowed to a spender.
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* @param owner address The address which owns the funds.
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* @param spender address The address which will spend the funds.
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* @return A uint256 specifying the amount of tokens still available for the spender.
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*/
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function allowance(address owner, address spender) public view returns (uint256) {
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return _allowances[owner][spender];
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}
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/**
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* @dev Transfer tokens from one address to another.
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* Note that while this function emits an Approval event, this is not required as per the specification,
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* and other compliant implementations may not emit the event.
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* @param from address The address which you want to send tokens from
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* @param to address The address which you want to transfer to
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* @param value uint256 the amount of tokens to be transferred
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*/
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function transferFrom(address from, address to, uint256 value) public returns (bool) {
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_transfer(from, to, value);
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_approve(from, msg.sender, _allowances[from][msg.sender].sub(value));
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return true;
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}
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/**
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* @dev Increase the amount of tokens that an owner allowed to a spender.
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* approve should be called when _allowances[msg.sender][spender] == 0. To increment
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* allowed value is better to use this function to avoid 2 calls (and wait until
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* the first transaction is mined)
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* From MonolithDAO Token.sol
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* Emits an Approval event.
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* @param spender The address which will spend the funds.
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* @param addedValue The amount of tokens to increase the allowance by.
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*/
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function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
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_approve(msg.sender, spender, _allowances[msg.sender][spender].add(addedValue));
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return true;
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}
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/**
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* @dev Decrease the amount of tokens that an owner allowed to a spender.
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* approve should be called when _allowances[msg.sender][spender] == 0. To decrement
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* allowed value is better to use this function to avoid 2 calls (and wait until
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* the first transaction is mined)
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* From MonolithDAO Token.sol
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* Emits an Approval event.
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* @param spender The address which will spend the funds.
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* @param subtractedValue The amount of tokens to decrease the allowance by.
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*/
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function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
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_approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue));
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return true;
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}
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/**
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* @dev Returns the amount of tokens in existence.
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*
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* See `IERC20.totalSupply`.
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*/
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function totalSupply() public view returns (uint256) {
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return _totalSupply;
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}
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/**
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* @dev Transfer token for a specified addresses.
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* @param from The address to transfer from.
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* @param to The address to transfer to.
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* @param value The amount to be transferred.
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*/
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function _transfer(address from, address to, uint256 value) internal {
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require(to != address(0), "ERC20: transfer to the zero address");
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_balances[from] = _balances[from].sub(value);
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_balances[to] = _balances[to].add(value);
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emit Transfer(from, to, value);
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}
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/**
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* @dev Internal function that mints an amount of the token and assigns it to
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* an account. This encapsulates the modification of balances such that the
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* proper events are emitted.
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* @param account The account that will receive the created tokens.
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* @param value The amount that will be created.
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*/
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function _mint(address account, uint256 value) internal {
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require(account != address(0), "ERC20: mint to the zero address");
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_totalSupply = _totalSupply.add(value);
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_balances[account] = _balances[account].add(value);
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emit Transfer(address(0), account, value);
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}
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/**
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* @dev Internal function that burns an amount of the token of a given
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* account.
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* @param account The account whose tokens will be burnt.
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* @param value The amount that will be burnt.
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*/
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function _burn(address account, uint256 value) internal {
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require(account != address(0), "ERC20: burn from the zero address");
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_totalSupply = _totalSupply.sub(value);
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_balances[account] = _balances[account].sub(value);
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emit Transfer(account, address(0), value);
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}
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/**
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* @dev Approve an address to spend another addresses' tokens.
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* @param owner The address that owns the tokens.
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* @param spender The address that will spend the tokens.
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* @param value The number of tokens that can be spent.
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*/
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function _approve(address owner, address spender, uint256 value) internal {
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require(owner != address(0), "ERC20: approve from the zero address");
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require(spender != address(0), "ERC20: approve to the zero address");
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_allowances[owner][spender] = value;
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emit Approval(owner, spender, value);
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}
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/**
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* @dev Internal function that burns an amount of the token of a given
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* account, deducting from the sender's allowance for said account. Uses the
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* internal burn function.
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* Emits an Approval event (reflecting the reduced allowance).
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* @param account The account whose tokens will be burnt.
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* @param value The amount that will be burnt.
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*/
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function _burnFrom(address account, uint256 value) internal {
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_burn(account, value);
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_approve(account, msg.sender, _allowances[account][msg.sender].sub(value));
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}
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}
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