Index

Chapter 12: Handling Multiple Return Values

This getKitty function is the first example we've seen that returns multiple values. Let's look at how to handle them:

Put it to the test

Time to interact with the CryptoKitties contract!
Let's make a function that gets the kitty genes from the contract:
1. Make a function called feedOnKitty. It will take 2 uint parameters, _zombieId and _kittyId, and should be a public function.

2. The function should first declare a uint named kittyDna.
Note: In our KittyInterface, genes is a uint256 — but if you remember back to lesson 1, uint is an alias for uint256 — they're the same thing.

3. The function should then call the kittyContract.getKitty function with _kittyIdand store genes in kittyDna. Remember — getKitty returns a ton of variables. (10 to be exact — I'm nice, I counted them for you!). But all we care about is the last one, genes. Count your commas carefully!

4. Finally, the function should call feedAndMultiply, and pass it both _zombieId and kittyDna.

function feedonKitty(uint _zombieId, uint _kittyId) public {
    uint kittyDna;
    (,,,,,,,,,kittyDna) = kittyContract.getKitty(_kittyId);
    feedAndMultiply(_zombieId, kittyDna);
  }

pragma solidity ^0.4.25;

import "./zombiefactory.sol";

contract KittyInterface {
  function getKitty(uint256 _id) external view returns (
    bool isGestating,
    bool isReady,
    uint256 cooldownIndex,
    uint256 nextActionAt,
    uint256 siringWithId,
    uint256 birthTime,
    uint256 matronId,
    uint256 sireId,
    uint256 generation,
    uint256 genes
  );
}

contract ZombieFeeding is ZombieFactory {

  address ckAddress = 0x06012c8cf97BEaD5deAe237070F9587f8E7A266d;
  KittyInterface kittyContract = KittyInterface(ckAddress);

  function feedAndMultiply(uint _zombieId, uint _targetDna) public {
    require(msg.sender == zombieToOwner[_zombieId]);
    Zombie storage myZombie = zombies[_zombieId];
    _targetDna = _targetDna % dnaModulus;
    uint newDna = (myZombie.dna + _targetDna) / 2;
    _createZombie("NoName", newDna);
  }

  function feedonKitty(uint _zombieId, uint _kittyId) public {
    uint kittyDna;
    (,,,,,,,,,kittyDna) = kittyContract.getKitty(_kittyId);
    feedAndMultiply(_zombieId, kittyDna);
  }

}