ERC-165

Standard Interface Detection

ERC165 is a standard to detect and publish what interfaces a smart contract implements.

Motivation

• Creates a standard method to publish and detect what interfaces a smart contract implements.

• This helps prevent tokens from getting stuck, when they are sent to contracts which do not support that token

• Like sending ERC20 to contracts that does not support ERC20, so they get stuck.

• We need to know if the necessary methods exist on the target function

Solution

• Keccak256 and XOR

• Keccak256(method_1) ^ Keccak256(method_2) ^ Keccak256(method_3)

• we will hash all the methods of an interface and XOR them -> with XOR the order will not matter

• you can think of this hexadecimal as the bytes4 fingerprint of an interface or group of methods.

This gives us a way to ask a contract "Do you support 0x780e9d63 (ERC721 Enumerable)?"

Calculating Interface ID

• interfaceid: type(IERC721).interfaceId

Example Implementation

• Inherit ERC165.sol

• override the supportsInterface function accordingly

In ERC165:

https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/introspection/ERC165.sol

In ERC721:

https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC721/ERC721.sol

• we override the inherited function on ERC165 and IERC165

• the child implementation checks for support on ERC712, ERC712Metadata, and ERC165 (super.supportsInterface)

Links

• https://medium.com/quick-programming/what-is-erc165-and-why-you-should-use-it-d0641a2f29e5

• https://www.youtube.com/watch?v=eXNcCJbFkN8