Index

Chapter 9: Zombie Modifiers

Now let's use our aboveLevel modifier to create some functions.
Our game will have some incentives for people to level up their zombies:
• For zombies level 2 and higher, users will be able to change their name.
• For zombies level 20 and higher, users will be able to give them custom DNA.
We'll implement these functions below. Here's the example code from the previous lesson for reference:

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

// Require that this user 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)
function driveCar(uint _userId) public olderThan(16, _userId) {
// Some function logic
}

Put it to the test

1. Create a function called changeName. It will take 2 arguments: _zombieId (a uint), and _newName (a string), and make it external. It should have the aboveLevel modifier, and should pass in 2 for the _level parameter. (Don't forget to also pass the _zombieId).

2. In this function, first we need to verify that msg.sender is equal to zombieToOwner[_zombieId]. Use a require statement.

3. Then the function should set zombies[_zombieId].name equal to _newName.

4. Create another function named changeDna below changeName. Its definition and contents will be almost identical to changeName, except its second argument will be _newDna (a uint), and it should pass in 20 for the _level parameter on aboveLevel. And of course, it should set the zombie's dna to _newDna instead of setting the zombie's name.

pragma solidity ^0.4.25;

import "./zombiefeeding.sol";

contract ZombieHelper is ZombieFeeding {

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

  // Start here
  function changeName(uint _zombieId, string _newName) external aboveLevel(2, _zombieId) {
    require(msg.sender == zombieToOwner[_zombieId]);
    zombies[_zombieId].name = _newName;
  }

  function changeDna(uint _zombieId, uint _newDna) external aboveLevel(20, _zombieId) {
    require(msg.sender == zombieToOwner[_zombieId]);
    zombies[_zombieId].dna = _newDna;

  }

}