Solidity get interface id and ERC165

To get interface id, use

type(ITest).interfaceId

Remember interfaceId = xor of all selectors (methods) name and param type, don't care to return type

For example:

• Return zero with empty interface

=> bytes4: 0x00000000
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
interface ITest {
}
contract Test is ITest {
    bytes4 public constant IID_ITEST = type(ITest).interfaceId;    
}

• Return same id with difference return type

=> bytes4: 0x0ee2cb10
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
interface ITest {
    function getCreator() external;
}
contract Test is ITest {
    bytes4 public constant IID_ITEST = type(ITest).interfaceId;   
    
    function getCreator() external override { } 
}
===========
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
interface ITest {
    function getCreator() external returns (uint);
}
contract Test is ITest {
    bytes4 public constant IID_ITEST = type(ITest).interfaceId;   
    
    function getCreator() external pure override returns (uint) {…