# EIP165 Standard Interface Detection

## Simple explanation

Interface Detection Standard creates a simple way for a contract to tell consumers (website or contracts or application) that it supports a specific set of functionalities. For example ERC21 metadata or EIP1155 etc.

This EIP Standardize following:

1. How interfaces are identified
2. How a contract will publish the interfaces it implements
3. How to detect if a contract implements ERC-165
4. How to detect if a contract implements any given interface

## Functions

`interface`\
Interfaces are identified by set of function selectors which are defined by the Ethereum ABI. It is a subset of Solidity's concept interfaces which defines return types, mutability and identifier.

`0x01ffc9a7`\
Interface identifier for this interface. You can calculate this by running `bytes4(keccak256('supportsInterface(bytes4)'));` or using the `Selector` contract

"How to Detect if a Contract Implements ERC-165

1. The source contract makes a `STATICCALL` to the destination address with input data: `0x01ffc9a701ffc9a700000000000000000000000000000000000000000000000000000000` and gas 30,000. This corresponds to `contract.supportsInterface(0x01ffc9a7)`.
2. If the call fails or return false, the destination contract does not implement ERC-165.
3. If the call returns true, a second call is made with input data `0x01ffc9a7ffffffff00000000000000000000000000000000000000000000000000000000`.
4. If the second call fails or returns true, the destination contract does not implement ERC-165.
5. Otherwise it implements ERC-165.

How to Detect if a Contract Implements any Given Interface

1. If you are not sure if the contract implements ERC-165, use the above procedure to confirm.
2. If it does not implement ERC-165, then you will have to see what methods it uses the old-fashioned way.
3. If it implements ERC-165 then just call `supportsInterface(interfaceID)` to determine if it implements an interface you can use."- EIP

## Further reading

* Full implementation: <https://eips.ethereum.org/EIPS/eip-165>


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