// contracts/StoreReader.sol
pragma solidity 0.5.8;
import "./StoreInterface.sol";
contract StoreReader is StoreInterfaceId {
  function getStoreValue(address store) external view returns (uint256) {
    if (ERC165(storeAddress).supportsInterface(0x75b24222)) {
      return store.getValue();
    }
    revert(“Doesn’t support StoreInterface”)
  }
}

// StoreInterface.sol
pragma solidity 0.5.8;
contract StoreInterfaceId {
  // StoreInterface.getValue.selector ^ StoreInterface.setValue.selector
  bytes4 internal constant STORE_INTERFACE_ID = 0x75b24222;
}
contract StoreInterface is StoreInterfaceId {
  function getValue() external view returns (uint256);
  function setValue(uint256 v) external;
}

// StoreReader.sol
pragma solidity 0.5.8;
import "./StoreInterface.sol";
import "./ERC165/ERC165Query.sol";
contract StoreReader is StoreInterfaceId, ERC165Query {
  StoreInterface store;
  constructor (address storeAddress) public {
    require(doesContractImplementInterface(
      storeAddress, STORE_INTERFACE_ID), 
      "Doesn't support StoreInterface");
    store = StoreInterface(storeAddress);
  }
  function readStoreValue() external view returns (uint256) {
    return store.getValue();
  }
}

// Selector.sol
pragma solidity 0.5.8;
import "./StoreInterface.sol";
contract Selector {
  // 0x75b24222
  function calcStoreInterfaceId() external pure returns (bytes4) {
    StoreInterface i;
    return i.getValue.selector ^ i.setValue.selector;
  }
}