Skip to main content

Standard Interface Detection Interface (TIP-6.1)

Simple summary​

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

Abstract​

Herein, we standardize the following:

  • How interfaces are identified
  • How a contract will publish the interfaces it implements

Motivation​

For some “standard interfaces” like the token interface, 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. This proposal standardizes the concept of interfaces and standardizes the identification (naming) of interfaces.

Specification​

How interfaces are identified​

For this standard, an interface is a set of function selectors as defined by the Solidity ABI. This a subset of Solidity’s concept of interfaces and the interface keyword definition which also defines return types, mutability and events.

We define the interface identifier as the XOR of all function selectors in the interface. This code example shows how to calculate an interface identifier:

Solidity​

interface Solidity101 {
    function hello() external pure;
    function world(int) external pure;
}

contract Selector {
    function calculateSelector() public view returns (bytes4) {
        Solidity101 i;
        return bytes4(tvm.functionId(i.hello) ^ tvm.functionId(i.world));
    }
}

How a Contract will Publish the Interfaces it Implements​

A contract that is compliant with TIP6.1 shall implement the following interface:

Solidity​

interface TIP6 {
    /// @notice Query if a contract implements an interface
    /// @param interfaceID The interface identifier, as specified in TIP6.1
    /// @dev Interface identification is specified in TIP6.1.
    /// @return `true` if the contract implements `interfaceID` and
    ///  `interfaceID` is not 0xffffffff, `false` otherwise
    function supportsInterface(bytes4 interfaceID) external view responsible returns (bool);
}

The interface identifier for this interface is 0x3204EC29. You can calculate this by running tvm.functionId('supportsInterface(bytes4)'); or using the Selector contract above.

Therefore, the implementing contract will have a supportsInterface function that returns:

  • true when interfaceID is 0x3204EC29 (TIP6.1 interface)
  • false when interfaceID is 0xffffffff
  • true for any other interfaceID this contract implements
  • false for any other interfaceID

References​