Nouns DAO contest - Polandia94's results

the function _beforeTokenTransfer from contracts/base/ERC721Enumerable.sol is called in three places, if we move the logic from _beforeTokenTransfer to _mint, _transfer, _burn four checks on every transfer will be eliminated.

we need to remove lines 81-113 from contracts/base/ERC721Enumerable.sol and replace with

 
    function _transfer(
        address from,
        address to,
        uint256 tokenId
    ) internal virtual override{
        if (to != from) {
            _removeTokenFromOwnerEnumeration(from, tokenId); // because to and from are != 0 and to !=from 
            _addTokenToOwnerEnumeration(to, tokenId); // because to and from are != 0 and to !=from 
        }
        super._transfer(from, to, tokenId);
    }

    function _mint(
        address creator,
        address to,
        uint256 tokenId
    ) internal virtual override{
        _addTokenToAllTokensEnumeration(tokenId); // because from == 0
        _addTokenToOwnerEnumeration(to, tokenId); // because to to !=from, to can't be 0
        super._mint(creator, to, tokenId);
    }

    function _burn(uint256 tokenId) internal virtual override{
        _removeTokenFromOwnerEnumeration(ownerOf(tokenId), tokenId); / because to to !=from, from can't be 0
        _removeTokenFromAllTokensEnumeration(tokenId); // because to == 0
        super._burn(tokenId);
        
    }

because in mint, burn and transfer we know if the from and to are the 0 address, so its not necessary to check at runtime(because it's not allowed transfer to the 0 address or mint to the 0 address in the ERC721.sol contract)