基础的定义必须先于派生合约的定义（ERC721 实现）

Question

前 or ETH Stack Exchange 个答案似乎不适用于我的情况（当然我可能是错的）

我在这个文件的标题中得到了错误描述符：

// 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) {}
}

这是 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;
    }
}

这是 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

您的 ERC721 合同中是否需要导入 ERC721Connector 合同？如果没有，您可以删除

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

来自您的文件，它应该可以正常工作。您的导入导致了问题，

ERC721Connector 尝试导入 ERC721，但是 ERC721 还需要 ERC721Connector 所以编译器说

Definition of base has to precede definition of derived contract

因为基础合同不先于定义的合同。

基础的定义必须先于派生合约的定义（ERC721 实现）

Definition of base has to precede definition of derived contract (ERC721 implementation)

solidity

smartcontracts

erc721