# ERC165 解读

*ERC165合约的个人解读*

By [Confucian](https://paragraph.com/@confucian) · 2022-11-01

smartcontract

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ERC165解读
========

参考 [OpenZeppelin文档](https://docs.openzeppelin.com/contracts/4.x/api/utils#IERC165) 并结合自己的理解

什么是ERC165
---------

一种用来检测合约所继承接口的标准方法。[EIP-165](https://github.com/ethereum/EIPs/blob/master/EIPS/eip-165.md) 中提出。

为什么要遵守ERC165
------------

EIP-165 中的动机：

> For some "standard interfaces" like [the ERC-20 token interface](https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md), it is sometimes useful to query whether a contract supports the interface and if yes, which version of the interface, in order to adapt the way in which the contract is to be interacted with. Specifically for ERC-20, a version identifier has already been proposed. This proposal standardizes the concept of interfaces and standardizes the identification (naming) of interfaces.

继承了 ERC165 的合约方便他人快速检测其实现了哪些接口。

代码实现
----

需实现以下函数：

    function supportsInterface(interfaceId)

### **IERC165**

    import "@openzeppelin/contracts/utils/introspection/IERC165.sol";

    // SPDX-License-Identifier: MIT
    pragma solidity ^0.8.0;
    
    interface IERC165 {
        function supportsInterface(bytes4 interfaceId) external view returns (bool);
    }

如果合约实现了 `interfaceId` 定义的接口，则返回 `true`

### **ERC165**

    import "@openzeppelin/contracts/utils/introspection/ERC165.sol";

    // SPDX-License-Identifier: MIT
    pragma solidity ^0.8.0;
    
    import "./IERC165.sol";
    
    abstract contract ERC165 is IERC165 {
        function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
            return interfaceId == type(IERC165).interfaceId;
        }
    }

#### **补充**

表达式 `type(x)` 可以检测参数 `x` 的类型信息。

接口类型的特别属性：

`type(I).interfaceId` :

*   返回接口 `I` 的 `bytes4` 类型的接口 ID，接口 ID 被定义为 `XOR` (异或) 接口内所有函数的函数选择器(function selector)。
    

**实际使用**
--------

ERC721合约中对ERC165的重写：

    function supportsInterface(bytes4 interfaceId) public view virtual override(ERC165, IERC165) returns (bool) {
        return
            interfaceId == type(IERC721).interfaceId ||
            interfaceId == type(IERC721Metadata).interfaceId ||
            super.supportsInterface(interfaceId);
    }

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*Originally published on [Confucian](https://paragraph.com/@confucian/erc165)*