Solidity Callbacks

callback.sol

pragma solidity ^0.4.24;


contract Data {
    address[] investors;

    function addData(uint256 _iters) public {
        for (uint256 i = 0; i < _iters; i++) {
            investors.push(address(i));
        }
    }
    
    function apply(uint256 _start, uint256 _end, function(address) external _callback) public {
        for (uint256 i = _start; i < _end; i++) {
            _callback(investors[i]);
        }
    }
}

contract Worker {
    
    address public dataAddress;

    event Log(address _sender, address _contract, address _investor);

    constructor(address _dataAddress) public {
        dataAddress = _dataAddress;
    }
    
    function applyWork(uint256 _start, uint256 _end) public {
        Data(dataAddress).apply(_start, _end, this.callback);
    }
    
    function callback(address _investor) external {
        emit Log(msg.sender, address(this), _investor);
    }
}