Make Structs, Enums, Constructors and Mappings work together - struct

Question

So I want to implement a simple CarShop contract in Solidity.
The contract should be initiated with a constructor where I input the current stock amount for the cars I already have in my Shop. I call these in the constructor (ToyotaCount, AudiCount, BmwCount)...
Then I think I need to create a struct that would store the CarCount and the CarType.
So I created an enum with (Toyota, Audi, Bmw)...
Finally, I would like to create this struct with the values CarCount from the constructor (as the initial state) together with carType of the cars from the enum... However, I am confused how exactly I should implement it and where I am going wrong.
Also, as a next step I want to implement a function called "AddCar" to update the values in the struct when I add some cars... for example I want to add 3 Audi cars...
Can you perhaps show me how I would need to correct my code, so the constructor, struct, enum work together. I would also really appreciate if you could point me to some similar projects or implementations.
This is my current Code. I think I initiated the constructor correctly. However, then something goes wrong with the interplay of struct and enum and constructor.
'''
contract CarShop {
address owner;
uint256 toyotaCount;
uint256 audiCount;
uint256 bmwCount;
constructor(uint256 _toyotaCount, uint256 _audiCount, uint256 _bmwCount) {
owner = msg.sender;
toyotaCount = _toyotaCount;
audiCount = _audiCount;
bmwCount = _bmwCount;
}
enum CarType {None, Toyota, Audi, Bmw}
struct Cars {
CarType carType;
uint count;
}
Cars public item;
Cars memory toyota = Cars(carType, toyotaCount)
}
'''

Answer 1

I made some changes to your contract and added some comments. Note that you should change how the cars are stored, because we use three Cars structs for the three different cars.
contract CarShop {
address owner;
uint256 toyotaCount;
uint256 audiCount;
uint256 bmwCount;
Cars public toyota;
Cars public audi;
Cars public bmw;
enum CarType {Toyota, Audi, Bmw}
struct Cars {
CarType carType;
uint count;
}
constructor(uint256 _toyotaCount, uint256 _audiCount, uint256 _bmwCount) {
owner = msg.sender;
toyotaCount = _toyotaCount;
audiCount = _audiCount;
bmwCount = _bmwCount;
// initialize the three cars with their count
toyota = Cars(CarType.Toyota, _toyotaCount);
audi = Cars(CarType.Audi, _audiCount);
bmw = Cars(CarType.Bmw, _bmwCount);
}
/**
* #dev Add car count function
* #param _carType type of the car: 0 for Toyota, 1 for Audi, 2 for Bmw
* #return _count increment car count
*/
function addCarCount(CarType _carType, uint256 _count) public {
require(msg.sender == owner, "Only owner can add car count");
if(_carType == CarType.Toyota) {
toyota.count += _count;
} else if(_carType == CarType.Audi) {
audi.count += _count;
} else if(_carType == CarType.Bmw) {
bmw.count += _count;
}
}
}
I deployed the contract with each 10 cars in store. I created a script that adds 3 cars to the audi struct.
import { ethers } from "hardhat";
async function main() {
const [owner] = await ethers.getSigners();
const contractAddress = process.env.CAR_CONTRACT_ADDRESS;
const contract = await ethers.getContractFactory("CarShop");
const contractInstance = await contract.attach(`${contractAddress}`);
const audi = await contractInstance.audi();
console.log(audi);
await contractInstance.connect(owner).addCarCount(1, 3);
const audiAfter = await contractInstance.audi();
console.log(audiAfter);
}
main().catch((error) => {
console.error(error);
process.exitCode = 1;
});
Results:
[
1,
BigNumber { value: "10" },
carType: 1,
count: BigNumber { value: "10" }
]
[
1,
BigNumber { value: "13" },
carType: 1,
count: BigNumber { value: "13" }
]

Answer 2

you cannot declare a memory variable in the contract level only in a function
Cars memory toyota = Cars(carType, toyotaCount)