基础的定义必须先于派生合同的定义(ERC721实现)

Question

顶级SO或ETH堆栈交换答案似乎不适用于我的情况(当然我可能错了(

我在这个文件的标题中得到了错误描述器：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "./ERC721Metadata.sol";
import "./ERC721.sol";
contract ERC721Connector is ERC721Metadata, ERC721 {
// ^^^^^^^ (Definition of base has to precede definition of derived contract)
constructor(string memory name, string memory symbol) ERC721Metadata(name, symbol) {}
}

以下是ERC721Metadadata的样子：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
contract ERC721Metadata {
string private _name;
string private _symbol;
constructor(string memory named, string memory symbolified) {
_name = named;
_symbol = symbolified;
}
function name() external view returns (string memory) {
return _name;
}
function symbol() external view returns (string memory) {
return _symbol;
}
}

以下是ERC721的样子：

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "./ERC721Metadata.sol";
import "./ERC721Connector.sol";
contract ERC721 {
event Transfer(
address indexed from,
address indexed to,
uint256 indexed tokenId
);
mapping(uint256 => address) private _tokenOwner;
mapping(address => uint256) private _OwnedTokensCount;
function _exists(uint256 tokenId) internal view returns (bool) {
address owner = _tokenOwner[tokenId];
return owner != address(0);
}
function _mint(address to, uint256 tokenId) internal {
require(to != address(0), "ERC721: minting to the zero address");
require(
!_exists(tokenId),
"ERC721: minting a token that already exists (been minted)"
);
_tokenOwner[tokenId] = to;
_OwnedTokensCount[to] += 1;
emit Transfer(address(0), to, tokenId);
}
}

Answer 1

是否需要在ERC721合同中导入ERC721Connector合同？如果没有，你可以删除

import "./ERC721Connector.sol"; // line 4, ERC721.sol

从你的文件中，它应该可以正常工作。，问题出在你的进口产品上

ERC721Connector试图导入ERC721，但ERC721也需要ERC721Connector，所以编译器说

基础的定义必须先于派生合同的定义

因为基本合约不在定义的合约之前。