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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,24 +1,37 @@ | ||
| pragma solidity ^0.5.2; | ||
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| import "../math/SafeMath.sol"; | ||
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| /** | ||
| * @title Counters | ||
| * @author Matt Condon (@shrugs) | ||
| * @dev Provides an incrementing uint256 id acquired by the `Counter#next` getter. | ||
| * Use this for issuing ERC721 ids or keeping track of request ids, anything you want, really. | ||
| * @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;` | ||
| * @notice Does not allow an Id of 0, which is popularly used to signify a null state in solidity. | ||
| * Does not protect from overflows, but if you have 2^256 ids, you have other problems. | ||
| * (But actually, it's generally impossible to increment a counter this many times, energy wise | ||
| * so it's not something you have to worry about.) | ||
| * Include with `using Counter for Counter.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; | ||
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| struct Counter { | ||
| uint256 current; // default: 0 | ||
| // 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 | ||
| } | ||
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| function current(Counter storage counter) internal view returns (uint256) { | ||
| return counter._value; | ||
| } | ||
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| function increment(Counter storage counter) internal { | ||
| counter._value += 1; | ||
| } | ||
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| function next(Counter storage index) internal returns (uint256) { | ||
| index.current += 1; | ||
| return index.current; | ||
| function decrement(Counter storage counter) internal { | ||
| counter._value = counter._value.sub(1); | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,37 +1,58 @@ | ||
| const { BN } = require('openzeppelin-test-helpers'); | ||
| const { shouldFail } = require('openzeppelin-test-helpers'); | ||
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| const CountersImpl = artifacts.require('CountersImpl'); | ||
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| const EXPECTED = [new BN(1), new BN(2), new BN(3), new BN(4)]; | ||
| const KEY1 = web3.utils.sha3('key1'); | ||
| const KEY2 = web3.utils.sha3('key2'); | ||
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| contract('Counters', function ([_, owner]) { | ||
| contract('Counters', function () { | ||
| beforeEach(async function () { | ||
| this.mock = await CountersImpl.new({ from: owner }); | ||
| this.counter = await CountersImpl.new(); | ||
| }); | ||
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| it('starts at zero', async function () { | ||
| (await this.counter.current()).should.be.bignumber.equal('0'); | ||
| }); | ||
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| context('custom key', async function () { | ||
| it('should return expected values', async function () { | ||
| for (const expectedId of EXPECTED) { | ||
| await this.mock.doThing(KEY1, { from: owner }); | ||
| const actualId = await this.mock.theId(); | ||
| actualId.should.be.bignumber.equal(expectedId); | ||
| } | ||
| describe('increment', function () { | ||
| it('increments the current value by one', async function () { | ||
| await this.counter.increment(); | ||
| (await this.counter.current()).should.be.bignumber.equal('1'); | ||
| }); | ||
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| it('can be called multiple times', async function () { | ||
| await this.counter.increment(); | ||
| await this.counter.increment(); | ||
| await this.counter.increment(); | ||
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| (await this.counter.current()).should.be.bignumber.equal('3'); | ||
| }); | ||
| }); | ||
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| context('parallel keys', async function () { | ||
| it('should return expected values for each counter', async function () { | ||
| for (const expectedId of EXPECTED) { | ||
| await this.mock.doThing(KEY1, { from: owner }); | ||
| let actualId = await this.mock.theId(); | ||
| actualId.should.be.bignumber.equal(expectedId); | ||
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| await this.mock.doThing(KEY2, { from: owner }); | ||
| actualId = await this.mock.theId(); | ||
| actualId.should.be.bignumber.equal(expectedId); | ||
| } | ||
| describe('decrement', function () { | ||
| beforeEach(async function () { | ||
| await this.counter.increment(); | ||
| (await this.counter.current()).should.be.bignumber.equal('1'); | ||
| }); | ||
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| it('decrements the current value by one', async function () { | ||
| await this.counter.decrement(); | ||
| (await this.counter.current()).should.be.bignumber.equal('0'); | ||
| }); | ||
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| it('reverts if the current value is 0', async function () { | ||
| await this.counter.decrement(); | ||
| await shouldFail.reverting(this.counter.decrement()); | ||
| }); | ||
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| it('can be called multiple times', async function () { | ||
| await this.counter.increment(); | ||
| await this.counter.increment(); | ||
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| (await this.counter.current()).should.be.bignumber.equal('3'); | ||
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| await this.counter.decrement(); | ||
| await this.counter.decrement(); | ||
| await this.counter.decrement(); | ||
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| (await this.counter.current()).should.be.bignumber.equal('0'); | ||
| }); | ||
| }); | ||
| }); |
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