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Implicitly clear ERC721 approval on transfers (OpenZeppelin#3481)
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Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
Co-authored-by: Francisco Giordano <frangio.1@gmail.com>
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3 people committed Sep 9, 2022
1 parent dc7ba09 commit 32076c9
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Showing 3 changed files with 6 additions and 5 deletions.
5 changes: 5 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -7,6 +7,11 @@
* `Address`: optimize `functionCall` functions by checking contract size only if there is no returned data. ([#3469](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3469))
* `GovernorCompatibilityBravo`: remove unused `using` statements ([#3506](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3506))
* `ERC20`: optimize `_transfer`, `_mint` and `_burn` by using `unchecked` arithmetic when possible. ([#3513](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3513))
* `ERC721`: optimize transfers by making approval clearing implicit instead of emitting an event. ([#3481](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3481))

### Compatibility Note

ERC-721 integrators that interpret contract state from events should make sure that they implement the clearing of approval that is implicit in every transfer according to the EIP. Previous versions of OpenZeppellin Contracts emitted an explicit `Approval` event even though it was not required by the specification, and this is no longer the case.

## 4.7.0 (2022-06-29)

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2 changes: 1 addition & 1 deletion contracts/token/ERC721/ERC721.sol
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Expand Up @@ -338,7 +338,7 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
_beforeTokenTransfer(from, to, tokenId);

// Clear approvals from the previous owner
_approve(address(0), tokenId);
delete _tokenApprovals[tokenId];

_balances[from] -= 1;
_balances[to] += 1;
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4 changes: 0 additions & 4 deletions test/token/ERC721/ERC721.behavior.js
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Expand Up @@ -96,10 +96,6 @@ function shouldBehaveLikeERC721 (errorPrefix, owner, newOwner, approved, another
expect(await this.token.getApproved(tokenId)).to.be.equal(ZERO_ADDRESS);
});

it('emits an Approval event', async function () {
expectEvent(receipt, 'Approval', { owner, approved: ZERO_ADDRESS, tokenId: tokenId });
});

it('adjusts owners balances', async function () {
expect(await this.token.balanceOf(owner)).to.be.bignumber.equal('1');
});
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