ContextSwitcher.sol

pragma solidity ^0.5.0;

contract Base {
  uint public num;
  address public sender;

  function setNum(uint _num) public {
    num = _num;
    sender = msg.sender;
  }
}

contract FirstCaller {
  uint public num;

  function setBaseNum(address _base, uint _num) public{
      Base base = Base(_base);
      base.setNum(_num);
  }

  function callSetNum(address _base, uint _num) public {
    (bool status, bytes memory returnData) = _base.call(abi.encodeWithSignature("setNum(uint256)", _num)); // Base's num is set 
  }

  function delegatecallSetNum(address _base, uint _num) public {
    (bool status, bytes memory returnData) = _base.delegatecall(abi.encodeWithSignature("setNum(uint256)", _num)); // Base's num is set 
  }
}

contract SecondCaller {
    function callThrough(FirstCaller _fc, Base _base, uint _num) public {
        _fc.delegatecallSetNum(address(_base), _num);
    }
}