QX ERC20
1.0.0
QX ERC20 Science Token /** *Submitted for verification at Etherscan.io on 2020-12-24 */
pragma solidity ^0.6.0;
/**
@dev Wrappers over Solidity's arithmetic operations with added overflow
checks.
Arithmetic operations in Solidity wrap on overflow. This can easily result
in bugs, because programmers usually assume that an overflow raises an
error, which is the standard behavior in high level programming languages.
SafeMath restores this intuition by reverting the transaction when an
operation overflows.
Using this library instead of the unchecked operations eliminates an entire
class of bugs, so it's recommended to use it always. / library SafeMath { /*
@dev Returns the addition of two unsigned integers, reverting on
overflow.
Counterpart to Solidity's + operator.
Requirements:
return c; }
/**
- operator./**
@dev Returns the subtraction of two unsigned integers, reverting with custom message on
overflow (when the result is negative).
Counterpart to Solidity's - operator.
Requirements:
return c; }
/**
@dev Returns the multiplication of two unsigned integers, reverting on
overflow.
Counterpart to Solidity's * operator.
Requirements:
uint256 c = a * b; require(c / a == b, "SafeMath: multiplication overflow");
return c; }
/**
/ operator. Note: this function uses arevert opcode (which leaves remaining gas untouched) while Solidity/**
@dev Returns the integer division of two unsigned integers. Reverts with custom message on
division by zero. The result is rounded towards zero.
Counterpart to Solidity's / operator. Note: this function uses a
revert opcode (which leaves remaining gas untouched) while Solidity
uses an invalid opcode to revert (consuming all remaining gas).
Requirements:
return c; }
/**
% operator. This function uses a revert/**
% operator. This function uses a revert// Partial License: MIT
pragma solidity ^0.6.0;
/**
@dev Standard math utilities missing in the Solidity language. / library Math { /*
/**
/**
// Partial License: MIT
pragma solidity ^0.6.0;
/**
@dev Searches a sorted array and returns the first index that contains
a value greater or equal to element. If no such index exists (i.e. all
values in the array are strictly less than element), the array length is
returned. Time complexity O(log n).
array is expected to be sorted in ascending order, and to contain no
repeated elements. */ function findUpperBound(uint256[] storage array, uint256 element) internal view returns (uint256) { if (array.length == 0) { return 0; }
uint256 low = 0; uint256 high = array.length;
while (low < high) { uint256 mid = Math.average(low, high);
// Note that mid will always be strictly less than high (i.e. it will be a valid array index)
// because Math.average rounds down (it does integer division with truncation).
if (array[mid] > element) {
high = mid;
} else {
low = mid + 1;
}
}
// At this point low is the exclusive upper bound. We will return the inclusive upper bound.
if (low > 0 && array[low - 1] == element) {
return low - 1;
} else {
return low;
}
}
}
// Partial License: MIT
pragma solidity ^0.6.0;
/**
@title Counters
@author Matt Condon (@shrugs)
@dev Provides counters that can only be incremented or decremented by one. This can be used e.g. to track the number
of elements in a mapping, issuing ERC721 ids, or counting request ids.
Include with using Counters for Counters.Counter;
Since it is not possible to overflow a 256 bit integer with increments of one, increment can skip the {SafeMath}
overflow check, thereby saving gas. This does assume however correct usage, in that the underlying _value is never
directly accessed. */ library Counters { using SafeMath for uint256;
struct Counter { // This variable should never be directly accessed by users of the library: interactions must be restricted to // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add // this feature: see ethereum/solidity#4637 uint256 _value; // default: 0 }
function current(Counter storage counter) internal view returns (uint256) { return counter._value; }
function increment(Counter storage counter) internal { // The {SafeMath} overflow check can be skipped here, see the comment at the top counter._value += 1; }
function decrement(Counter storage counter) internal { counter._value = counter._value.sub(1); } }
// Partial License: MIT
pragma solidity ^0.6.0;
/*
@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 GSN 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 payable) { return msg.sender; }
function _msgData() internal view virtual returns (bytes memory) { this; // silence state mutability warning without generating bytecode - see ethereum/solidity#2691 return msg.data; } }
// Partial License: MIT
pragma solidity ^0.6.0;
/**
@dev Interface of the ERC20 standard as defined in the EIP. / interface IERC20 { /*
/**
account.
*/
function balanceOf(address account) external view returns (uint256);/**
amount tokens from the caller's account to recipient./**
spender will beowner through {transferFrom}. This is/**
amount as the allowance of spender over the caller's tokens./**
amount tokens from sender to recipient using theamount is then deducted from the caller's/**
value tokens are moved from one account (from) toto).value may be zero.
*/
event Transfer(address indexed from, address indexed to, uint256 value);/**
spender for an owner is set byvalue is the new allowance.
*/
event Approval(address indexed owner, address indexed spender, uint256 value);
}// Partial License: MIT
pragma solidity ^0.6.2;
/**
@dev Collection of functions related to the address type / library Address { /*
@dev Returns true if account is a contract.
[IMPORTANT]
====
It is unsafe to assume that an address for which this function returns
false is an externally-owned account (EOA) and not a contract.
Among others, isContract will return false for the following
types of addresses:
==== */ function isContract(address account) internal view returns (bool) { // This method relies in extcodesize, which returns 0 for contracts in // construction, since the code is only stored at the end of the // constructor execution.
uint256 size; // solhint-disable-next-line no-inline-assembly assembly { size := extcodesize(account) } return size > 0; }
/**
@dev Replacement for Solidity's transfer: sends amount wei to
recipient, forwarding all available gas and reverting on errors.
https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
of certain opcodes, possibly making contracts go over the 2300 gas limit
imposed by transfer, making them unable to receive funds via
transfer. {sendValue} removes this limitation.
https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
IMPORTANT: because control is transferred to recipient, care must be
taken to not create reentrancy vulnerabilities. Consider using
{ReentrancyGuard} or the
https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern]. */ function sendValue(address payable recipient, uint256 amount) internal { require(address(this).balance >= amount, "Address: insufficient balance");
// solhint-disable-next-line avoid-low-level-calls, avoid-call-value (bool success, ) = recipient.call{ value: amount }(""); require(success, "Address: unable to send value, recipient may have reverted"); }
/**
call. Acall is an unsafe replacement for a function call: use thistarget reverts with a revert reason, it is bubbled up by thistarget must be a contract.target with data must not revert./**
functionCall], but witherrorMessage as a fallback revert reason when target reverts./**
functionCall],value wei to target.value.payable./**
functionCallWithValue], buterrorMessage as a fallback revert reason when target reverts.function _functionCallWithValue(address target, bytes memory data, uint256 weiValue, string memory errorMessage) private returns (bytes memory) { require(isContract(target), "Address: call to non-contract");
// solhint-disable-next-line avoid-low-level-calls
(bool success, bytes memory returndata) = target.call{ value: weiValue }(data);
if (success) {
return returndata;
} else {
// Look for revert reason and bubble it up if present
if (returndata.length > 0) {
// The easiest way to bubble the revert reason is using memory via assembly
// solhint-disable-next-line no-inline-assembly
assembly {
let returndata_size := mload(returndata)
revert(add(32, returndata), returndata_size)
}
} else {
revert(errorMessage);
}
}
} }
// Partial License: MIT
pragma solidity ^0.6.0;
/**
@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 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;
mapping (address => uint256) private _balances;
mapping (address => mapping (address => uint256)) private _allowances;
uint256 private _totalSupply;
string private _name; string private _symbol; uint8 private _decimals;
/**
/**
/**
/**
decimals equals 2, a balance of 505 tokens should5,05 (505 / 10 ** 2)./**
/**
/**
recipient cannot be the zero address.amount.
*/
function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
_transfer(_msgSender(), recipient, amount);
return true;
}/**
/**
spender cannot be the zero address.
*/
function approve(address spender, uint256 amount) public virtual override returns (bool) {
_approve(_msgSender(), spender, amount);
return true;
}/**
sender and recipient cannot be the zero address.sender must have a balance of at least amount.sender's tokens of at leastamount.
*/
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;
}/**
spender by the caller.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;
}/**
spender by the caller.spender cannot be the zero address.spender must have allowance for the caller of at leastsubtractedValue.
*/
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;
}/**
@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");_beforeTokenTransfer(sender, recipient, amount);
_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) internal virtual {
require(account != address(0), "ERC20: mint to the zero address");_beforeTokenTransfer(address(0), account, amount);
_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 virtual {
require(account != address(0), "ERC20: burn from the zero address");_beforeTokenTransfer(account, address(0), amount);
_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 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); }
/**
/**
from and to are both non-zero, amount of from's tokensto.from is zero, amount tokens will be minted for to.to is zero, amount of from's tokens will be burned.from and to are never both zero.// Partial License: MIT
pragma solidity ^0.6.0;
/**
@dev This contract extends an ERC20 token with a snapshot mechanism. When a snapshot is created, the balances and
total supply at the time are recorded for later access.
This can be used to safely create mechanisms based on token balances such as trustless dividends or weighted voting.
In naive implementations it's possible to perform a "double spend" attack by reusing the same balance from different
accounts. By using snapshots to calculate dividends or voting power, those attacks no longer apply. It can also be
used to create an efficient ERC20 forking mechanism.
Snapshots are created by the internal {_snapshot} function, which will emit the {Snapshot} event and return a
snapshot id. To get the total supply at the time of a snapshot, call the function {totalSupplyAt} with the snapshot
id. To get the balance of an account at the time of a snapshot, call the {balanceOfAt} function with the snapshot id
and the account address.
==== Gas Costs
Snapshots are efficient. Snapshot creation is O(1). Retrieval of balances or total supply from a snapshot is _O(log
n)_ in the number of snapshots that have been created, although n for a specific account will generally be much
smaller since identical balances in subsequent snapshots are stored as a single entry.
There is a constant overhead for normal ERC20 transfers due to the additional snapshot bookkeeping. This overhead is
only significant for the first transfer that immediately follows a snapshot for a particular account. Subsequent
transfers will have normal cost until the next snapshot, and so on. */ abstract contract ERC20Snapshot is ERC20 { // Inspired by Jordi Baylina's MiniMeToken to record historical balances: // https://github.com/Giveth/minimd/blob/ea04d950eea153a04c51fa510b068b9dded390cb/contracts/MiniMeToken.sol
using SafeMath for uint256; using Arrays for uint256[]; using Counters for Counters.Counter;
// Snapshotted values have arrays of ids and the value corresponding to that id. These could be an array of a // Snapshot struct, but that would impede usage of functions that work on an array. struct Snapshots { uint256[] ids; uint256[] values; }
mapping (address => Snapshots) private _accountBalanceSnapshots; Snapshots private _totalSupplySnapshots;
// Snapshot ids increase monotonically, with the first value being 1. An id of 0 is invalid. Counters.Counter private _currentSnapshotId;
/**
id is created.
*/
event Snapshot(uint256 id);/**
@dev Creates a new snapshot and returns its snapshot id.
Emits a {Snapshot} event that contains the same id.
{_snapshot} is internal and you have to decide how to expose it externally. Its usage may be restricted to a
set of accounts, for example using {AccessControl}, or it may be open to the public.
[WARNING]
====
While an open way of calling {_snapshot} is required for certain trust minimization mechanisms such as forking,
you must consider that it can potentially be used by attackers in two ways.
First, it can be used to increase the cost of retrieval of values from snapshots, although it will grow
logarithmically thus rendering this attack ineffective in the long term. Second, it can be used to target
specific accounts and increase the cost of ERC20 transfers for them, in the ways specified in the Gas Costs
section above.
We haven't measured the actual numbers; if this is something you're interested in please reach out to us.
==== */ function _snapshot() internal virtual returns (uint256) { _currentSnapshotId.increment();
uint256 currentId = _currentSnapshotId.current(); emit Snapshot(currentId); return currentId; }
/**
@dev Retrieves the balance of account at the time snapshotId was created.
*/
function balanceOfAt(address account, uint256 snapshotId) public view returns (uint256) {
(bool snapshotted, uint256 value) = _valueAt(snapshotId, _accountBalanceSnapshots[account]);
return snapshotted ? value : balanceOf(account); }
/**
@dev Retrieves the total supply at the time snapshotId was created.
*/
function totalSupplyAt(uint256 snapshotId) public view returns(uint256) {
(bool snapshotted, uint256 value) = _valueAt(snapshotId, _totalSupplySnapshots);
return snapshotted ? value : totalSupply(); }
// Update balance and/or total supply snapshots before the values are modified. This is implemented // in the _beforeTokenTransfer hook, which is executed for _mint, _burn, and _transfer operations. function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual override { super._beforeTokenTransfer(from, to, amount);
if (from == address(0)) { // mint _updateAccountSnapshot(to); _updateTotalSupplySnapshot(); } else if (to == address(0)) { // burn _updateAccountSnapshot(from); _updateTotalSupplySnapshot(); } else { // transfer _updateAccountSnapshot(from); _updateAccountSnapshot(to); } }
function _valueAt(uint256 snapshotId, Snapshots storage snapshots) private view returns (bool, uint256) { require(snapshotId > 0, "ERC20Snapshot: id is 0"); // solhint-disable-next-line max-line-length require(snapshotId <= _currentSnapshotId.current(), "ERC20Snapshot: nonexistent id");
// When a valid snapshot is queried, there are three possibilities:
// a) The queried value was not modified after the snapshot was taken. Therefore, a snapshot entry was never
// created for this id, and all stored snapshot ids are smaller than the requested one. The value that corresponds
// to this id is the current one.
// b) The queried value was modified after the snapshot was taken. Therefore, there will be an entry with the
// requested id, and its value is the one to return.
// c) More snapshots were created after the requested one, and the queried value was later modified. There will be
// no entry for the requested id: the value that corresponds to it is that of the smallest snapshot id that is
// larger than the requested one.
//
// In summary, we need to find an element in an array, returning the index of the smallest value that is larger if
// it is not found, unless said value doesn't exist (e.g. when all values are smaller). Arrays.findUpperBound does
// exactly this.
uint256 index = snapshots.ids.findUpperBound(snapshotId);
if (index == snapshots.ids.length) {
return (false, 0);
} else {
return (true, snapshots.values[index]);
}
}
function _updateAccountSnapshot(address account) private { _updateSnapshot(_accountBalanceSnapshots[account], balanceOf(account)); }
function _updateTotalSupplySnapshot() private { _updateSnapshot(_totalSupplySnapshots, totalSupply()); }
function _updateSnapshot(Snapshots storage snapshots, uint256 currentValue) private { uint256 currentId = _currentSnapshotId.current(); if (_lastSnapshotId(snapshots.ids) < currentId) { snapshots.ids.push(currentId); snapshots.values.push(currentValue); } }
function _lastSnapshotId(uint256[] storage ids) private view returns (uint256) { if (ids.length == 0) { return 0; } else { return ids[ids.length - 1]; } } }
// Partial License: MIT
pragma solidity ^0.6.0;
/**
@dev Library for managing
https://en.wikipedia.org/wiki/Set_(abstract_data_type)[sets] of primitive
types.
Sets have the following properties:
(O(1)).
contract Example {
// Add the library methods
using EnumerableSet for EnumerableSet.AddressSet;
// Declare a set state variable
EnumerableSet.AddressSet private mySet;
}
As of v3.0.0, only sets of type address (AddressSet) and uint256
(UintSet) are supported.
*/
library EnumerableSet {
// To implement this library for multiple types with as little code
// repetition as possible, we write it in terms of a generic Set type with
// bytes32 values.
// The Set implementation uses private functions, and user-facing
// implementations (such as AddressSet) are just wrappers around the
// underlying Set.
// This means that we can only create new EnumerableSets for types that fit
// in bytes32.
struct Set { // Storage of set values bytes32[] _values;
// Position of the value in the `values` array, plus 1 because index 0
// means a value is not in the set.
mapping (bytes32 => uint256) _indexes;
}
/**
/**
@dev Removes a value from a set. O(1).
Returns true if the value was removed from the set, that is if it was
present. */ function _remove(Set storage set, bytes32 value) private returns (bool) { // We read and store the value's index to prevent multiple reads from the same storage slot uint256 valueIndex = set._indexes[value];
if (valueIndex != 0) { // Equivalent to contains(set, value) // To delete an element from the _values array in O(1), we swap the element to delete with the last one in // the array, and then remove the last element (sometimes called as 'swap and pop'). // This modifies the order of the array, as noted in {at}.
uint256 toDeleteIndex = valueIndex - 1;
uint256 lastIndex = set._values.length - 1;
// When the value to delete is the last one, the swap operation is unnecessary. However, since this occurs
// so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.
bytes32 lastvalue = set._values[lastIndex];
// Move the last value to the index where the value to delete is
set._values[toDeleteIndex] = lastvalue;
// Update the index for the moved value
set._indexes[lastvalue] = toDeleteIndex + 1; // All indexes are 1-based
// Delete the slot where the moved value was stored
set._values.pop();
// Delete the index for the deleted slot
delete set._indexes[value];
return true;
} else { return false; } }
/**
/**
/**
index in the set. O(1).index must be strictly less than {length}.
*/
function _at(Set storage set, uint256 index) private view returns (bytes32) {
require(set._values.length > index, "EnumerableSet: index out of bounds");
return set._values[index];
}// AddressSet
struct AddressSet { Set _inner; }
/**
/**
/**
/**
/**
index in the set. O(1).index must be strictly less than {length}.
*/
function at(AddressSet storage set, uint256 index) internal view returns (address) {
return address(uint256(_at(set._inner, index)));
}// UintSet
struct UintSet { Set _inner; }
/**
/**
/**
/**
/**
index in the set. O(1).index must be strictly less than {length}.
*/
function at(UintSet storage set, uint256 index) internal view returns (uint256) {
return uint256(_at(set._inner, index));
}
}// Partial License: MIT
pragma solidity ^0.6.0;
/**
@dev Contract module that allows children to implement role-based access
control mechanisms.
Roles are referred to by their bytes32 identifier. These should be exposed
in the external API and be unique. The best way to achieve this is by
using public constant hash digests:
bytes32 public constant MY_ROLE = keccak256("MY_ROLE");
Roles can be used to represent a set of permissions. To restrict access to a
function call, use {hasRole}:
function foo() public {
require(hasRole(MY_ROLE, msg.sender));
...
}
Roles can be granted and revoked dynamically via the {grantRole} and
{revokeRole} functions. Each role has an associated admin role, and only
accounts that have a role's admin role can call {grantRole} and {revokeRole}.
By default, the admin role for all roles is DEFAULT_ADMIN_ROLE, which means
that only accounts with this role will be able to grant or revoke other
roles. More complex role relationships can be created by using
{_setRoleAdmin}.
WARNING: The DEFAULT_ADMIN_ROLE is also its own admin: it has permission to
grant and revoke this role. Extra precautions should be taken to secure
accounts that have been granted it. */ abstract contract AccessControl is Context { using EnumerableSet for EnumerableSet.AddressSet; using Address for address;
struct RoleData { EnumerableSet.AddressSet members; bytes32 adminRole; }
mapping (bytes32 => RoleData) private _roles;
bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;
/**
newAdminRole is set as role's admin role, replacing previousAdminRoleDEFAULT_ADMIN_ROLE is the starting admin for all roles, despite/**
account is granted role.sender is the account that originated the contract call, an admin role/**
account is revoked role.sender is the account that originated the contract call:revokeRole, it is the admin role bearerrenounceRole, it is the role bearer (i.e. account)
*/
event RoleRevoked(bytes32 indexed role, address indexed account, address indexed sender);/**
true if account has been granted role.
*/
function hasRole(bytes32 role, address account) public view returns (bool) {
return _roles[role].members.contains(account);
}/**
role. Can be used/**
role. index must be a/**
role. See {grantRole} and/**
@dev Grants role to account.
If account had not been already granted role, emits a {RoleGranted}
event.
Requirements:
role's admin role.
*/
function grantRole(bytes32 role, address account) public virtual {
require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to grant");_grantRole(role, account); }
/**
@dev Revokes role from account.
If account had been granted role, emits a {RoleRevoked} event.
Requirements:
role's admin role.
*/
function revokeRole(bytes32 role, address account) public virtual {
require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to revoke");_revokeRole(role, account); }
/**
@dev Revokes role from the calling account.
Roles are often managed via {grantRole} and {revokeRole}: this function's
purpose is to provide a mechanism for accounts to lose their privileges
if they are compromised (such as when a trusted device is misplaced).
If the calling account had been granted role, emits a {RoleRevoked}
event.
Requirements:
account.
*/
function renounceRole(bytes32 role, address account) public virtual {
require(account == _msgSender(), "AccessControl: can only renounce roles for self");_revokeRole(role, account); }
/**
role to account.account had not been already granted role, emits a {RoleGranted}/**
adminRole as role's admin role.function _grantRole(bytes32 role, address account) private { if (_roles[role].members.add(account)) { emit RoleGranted(role, account, _msgSender()); } }
function _revokeRole(bytes32 role, address account) private { if (_roles[role].members.remove(account)) { emit RoleRevoked(role, account, _msgSender()); } } }
pragma solidity 0.6.8;
contract QXToken is Context, AccessControl, ERC20Snapshot { bytes32 public constant SNAPSHOT_ROLE = keccak256("SNAPSHOT_ROLE");
constructor(uint256 amount, uint8 decimals) ERC20("QX ERC20", "QX") public {
_setupDecimals(decimals);
_mint(msg.sender, amount);
// set up required roles
_setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
_setupRole(SNAPSHOT_ROLE, _msgSender());
}
/**
* @dev Creates a new snapshot and returns its snapshot id.
* Emits a {Snapshot} event that contains the same id.
*/
function snapshot() public {
require(hasRole(SNAPSHOT_ROLE, _msgSender()), "Must have snapshot role to create a snapshot");
_snapshot();
}
}
