You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
40 lines
1.5 KiB
40 lines
1.5 KiB
// SPDX-License-Identifier: MIT
|
|
|
|
pragma solidity >=0.6.0 <0.8.0;
|
|
|
|
import "../math/SafeMath.sol";
|
|
|
|
/**
|
|
* @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 https://github.com/ethereum/solidity/issues/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);
|
|
}
|
|
}
|
|
|