[fix] 修复Solidity-103, 34课 ERC721 文档与示例代码不相符的问题.

[ramsayleung]

问题

文档与代码不相符

Solidity-103 34课 ERC271 文档描述 :

ERC721主合约实现了IERC721，IERC165和IERC721Metadata定义的所有功能，包含4个状态变量和17个函数:

但示例代码只声明了 IERC721 和 IERC721Metadata 接口, 并没有声明IERC165:

contract ERC721 is IERC721, IERC721Metadata{
...
    // 实现IERC165接口supportsInterface
    function supportsInterface(bytes4 interfaceId)
        external
        pure
        override
        returns (bool)
    {
        return
            interfaceId == type(IERC721).interfaceId ||
            interfaceId == type(IERC165).interfaceId ||
            interfaceId == type(IERC721Metadata).interfaceId;
    }
...
}

缺失上下文信息, 函数理解有难度

ERC721利用_checkOnERC721Received来确保目标合约实现了onERC721Received()函数（返回onERC721Received的selector)

function _checkOnERC721Received(
    address operator,
    address from,
    address to,
    uint256 tokenId,
    bytes memory data
) internal {
    if (to.code.length > 0) {
        try IERC721Receiver(to).onERC721Received(operator, from, tokenId, data) returns (bytes4 retval) {
            if (retval != IERC721Receiver.onERC721Received.selector) {
                // Token rejected
                revert IERC721Errors.ERC721InvalidReceiver(to);
            }
        } catch (bytes memory reason) {
        }
    }
}

_checkOnERC721Received 通过检查 onERC721Received的selector 来判断是否实现了OnERC721Received, 但是并没有提供上下文说明为什么可以这么判断, 不便于初学者理解

解决方案

1. 更新示例代码，保证文档与示例代码相符
2. 增加 OnERC721Received 函数的注释，以解释为什么可以通过"返回onERC721Received的selector"来判断是否实现了IERC721Receiver接口

[vercel]

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