Index

Chapter 8: More on Function Modifiers

Great! Our zombie now has a functional cooldown timer.
Next, we're going to add some additional helper methods. We've created a new file for you called zombiehelper.sol, which imports zombiefeeding.sol. This will help to keep our code organized.
Let's make it so zombies gain special abilities after reaching a certain level. But in order to do that, first we'll need to learn a little bit more about function modifiers.

Function modifiers with arguments

Previously we looked at the simple example of onlyOwner. But function modifiers can also take arguments. For example:

// A mapping to store a user's age:
mapping (uint => uint) public age;

// Modifier that requires this user to be older than a certain age:
modifier olderThan(uint _age, uint _userId) {
  require(age[_userId] >= _age);
  _;
}

// Must be older than 16 to drive a car (in the US, at least).
// We can call the `olderThan` modifier with arguments like so:
function driveCar(uint _userId) public olderThan(16, _userId) {
  // Some function logic
}

You can see here that the olderThan modifier takes arguments just like a function does. And that the driveCar function passes its arguments to the modifier.
Let's try making our own modifier that uses the zombie level property to restrict access to special abilities.

Put it to the test

1. In ZombieHelper, create a modifier called aboveLevel. It will take 2 arguments, _level (a uint) and _zombieId (also a uint).

2. The body should check to make sure zombies[_zombieId].level is greater than or equal to _level.

3. Remember to have the last line of the modifier call the rest of the function with _;.

pragma solidity ^0.4.25;

import "./zombiefeeding.sol";

contract ZombieHelper is ZombieFeeding {

  // Start here
  modifier aboveLevel(uint _level, uint _zombieId) {
    require(zombies[_zombieId].level >= _level);
    _;
  }

}