Elevator

This elevator won't let you reach the top of your building. Right?

• Sometimes a solidity contract or library
• This Elevator expects to be used from a Building.

TIP

You can use the view function modifier on an interface in order to prevent state modifications. The pure modifier also prevents functions from modifying the state. Make sure you read Solidity's documentation (opens new window) and learn its caveats.

An alternative way to solve this level is to build a view function which returns different results depends on input data but don't modify state, e.g. gasleft().

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

interface Building {
  function isLastFloor(uint) external returns (bool);
}


contract Elevator {
  bool public top;
  uint public floor;

  function goTo(uint _floor) public {
    Building building = Building(msg.sender);

    if (! building.isLastFloor(_floor)) {
      floor = _floor;
      top = building.isLastFloor(floor);
    }
  }
}