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38 lines
1.2 KiB
38 lines
1.2 KiB
// SPDX-License-Identifier: MIT
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pragma solidity ^0.8.0;
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/**
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* @title Counters
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* @author Matt Condon (@shrugs)
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* @dev Provides counters that can only be incremented or decremented by one. This can be used e.g. to track the number
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* of elements in a mapping, issuing ERC721 ids, or counting request ids.
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*
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* Include with `using Counters for Counters.Counter;`
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*/
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library Counters {
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struct Counter {
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// This variable should never be directly accessed by users of the library: interactions must be restricted to
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// the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
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// this feature: see https://github.com/ethereum/solidity/issues/4637
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uint256 _value; // default: 0
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}
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function current(Counter storage counter) internal view returns (uint256) {
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return counter._value;
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}
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function increment(Counter storage counter) internal {
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unchecked {
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counter._value += 1;
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}
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}
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function decrement(Counter storage counter) internal {
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uint256 value = counter._value;
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require(value > 0, "Counter: decrement overflow");
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unchecked {
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counter._value = value - 1;
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}
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}
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}
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