Index

Chapter 5: Inheritance

Our game code is getting quite long. Rather than making one extremely long contract, sometimes it makes sense to split your code logic across multiple contracts to organize the code.
One feature of Solidity that makes this more manageable is contract inheritance:

contract Doge {
  function catchphrase() public returns (string) {
    return "So Wow CryptoDoge";
  }
}

contract BabyDoge is Doge {
  function anotherCatchphrase() public returns (string) {
    return "Such Moon BabyDoge";
  }
}


BabyDoge

inherits from Doge. That means if you compile and deploy BabyDoge, it will have access to both catchphrase() and anotherCatchphrase() (and any other public functions we may define on Doge).
This can be used for logical inheritance (such as with a subclass, a Cat is an Animal). But it can also be used simply for organizing your code by grouping similar logic together into different contracts.

Put it to the test

In the next chapters, we're going to be implementing the functionality for our zombies to feed and multiply. Let's put this logic into its own contract that inherits all the methods from ZombieFactory.
1. Make a contract called ZombieFeeding below ZombieFactory. This contract should inherit from our ZombieFactory contract.

contract ZombieFeeding is ZombieFactory {

}

pragma solidity ^0.4.25;

contract ZombieFactory {

    event NewZombie(uint zombieId, string name, uint dna);

    uint dnaDigits = 16;
    uint dnaModulus = 10 ** dnaDigits;

    struct Zombie {
        string name;
        uint dna;
    }

    Zombie[] public zombies;

    mapping (uint => address) public zombieToOwner;
    mapping (address => uint) ownerZombieCount;

    function _createZombie(string _name, uint _dna) private {
        uint id = zombies.push(Zombie(_name, _dna)) - 1;
        zombieToOwner[id] = msg.sender;
        ownerZombieCount[msg.sender]++;
        emit NewZombie(id, _name, _dna);
    }

    function _generateRandomDna(string _str) private view returns (uint) {
        uint rand = uint(keccak256(abi.encodePacked(_str)));
        return rand % dnaModulus;
    }

    function createRandomZombie(string _name) public {
        require(ownerZombieCount[msg.sender] == 0);
        uint randDna = _generateRandomDna(_name);
        _createZombie(_name, randDna);
    }

}

contract ZombieFeeding is ZombieFactory {

}