ERC165Removable.sol

// SPDX-License-Identifier: MIT;

pragma solidity ^0.6.6;

import "./IERC165.sol";

/**
 * @dev Custom implementation of the IERC165 interface.
 * This is contract implemented by OpenZeppelin but extended with
 * _removeInterface function
 */
contract ERC165Removable is IERC165 {
  /**
    * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
    */
  bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;

  /**
    * @dev Mapping of interface ids to whether or not it's supported.
    */
  mapping(bytes4 => bool) private _supportedInterfaces;

  constructor () internal {
      // Derived contracts need only register support for their own interfaces,
      // we register support for ERC165 itself here
      _registerInterface(_INTERFACE_ID_ERC165);
  }

  /**
    * @dev See {IERC165-supportsInterface}.
    *
    * Time complexity O(1), guaranteed to always use less than 30 000 gas.
    */
  function supportsInterface(bytes4 interfaceId) public view override returns (bool) {
      return _supportedInterfaces[interfaceId];
  }

  /**
    * @dev Registers the contract as an implementer of the interface defined by
    * `interfaceId`. Support of the actual ERC165 interface is automatic and
    * registering its interface id is not required.
    *
    * See {IERC165-supportsInterface}.
    *
    * Requirements:
    *
    * - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
    */
  function _registerInterface(bytes4 interfaceId) internal virtual {
      require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
      _supportedInterfaces[interfaceId] = true;
  }

  /**
    * @dev Removes support of the interface
    * @param interfaceId Interface Id
    */
  function _removeInterface(bytes4 interfaceId) internal {
      require(_supportedInterfaces[interfaceId], "ERC165: unknown interface id");
      _supportedInterfaces[interfaceId] = false;
  }
}