33 lines
1.1 KiB
Solidity
33 lines
1.1 KiB
Solidity
// SPDX-License-Identifier: MIT
|
|
|
|
pragma solidity ^0.8.0;
|
|
|
|
/**
|
|
* @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;`
|
|
*/
|
|
library Counters {
|
|
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 {
|
|
counter._value += 1;
|
|
}
|
|
|
|
function decrement(Counter storage counter) internal {
|
|
counter._value = counter._value - 1;
|
|
}
|
|
}
|