Lesson9: confused with why Interactions.s.sol:AddConsumer is working with forked spolia test

[caodanbobo]

In section 'Forked test environment and dynamic private keys', we learnt that how to test with forked Sepolia network. I am confused why the 'addingCustomer' function is working in sepolia network.
In 'DeployRaffle', the deployed Raffle contract is added as a consumed of the vrf:

vm.startBroadcast();
        Raffle raffle = new Raffle(
            config.enteranceFee,
            config.interval,
            config.vrfCoordinator,
            config.keyHash,
            config.subId,
            config.callbackGasLimit
        );
        vm.stopBroadcast();

        AddConsumer addConsumer = new AddConsumer();
        addConsumer.addingConsumer(
            address(raffle),
            config.vrfCoordinator,
            config.subId
        );

but inside the function 'addingConsumer', the 'VRFCoordinatorV2_5Mock' is used in both local and sepolia test, and both are working, why?

function addingConsumer(
        address contractToVrf,
        address vrfCoodi,
        uint256 subId
    ) public {
        console.log("adding consumer contract: ", contractToVrf);
        console.log("using vrfCoodinator:", vrfCoodi);
        console.log("on chain id: ", block.chainid);
        vm.startBroadcast();
        VRFCoordinatorV2_5Mock(vrfCoodi).addConsumer(subId, contractToVrf);
        vm.stopBroadcast();
    }

this also apply to 'createSubscription' when the subid is equal to 0.

[EngrPips]

Hello @caodanbobo, So, to make a call to a contract on the blockchain, you need the address of the contract on the blockchain and the interface of the contract. So, let's understand why we need these two things.

We need the address of the contract on the blockchain so that we can send the transaction directly to it. It's like if I want to come and visit you in your house, I need the address of your house to come to your house.

We need the interface of the contract that we want to send a transaction to be able to call the correct function on the contract address that we have. Let's assume I am not just coming to your house to visit but to come to deliver a package. You have a very big house, and you can never know I have arrived to deliver the package except if I use the doorbell at your home. Now, let's assume you are using a special doorbell, which I don't know how to operate. I know I need to be able to use your doorbell if I want my delivery to be successful, so I will need to learn how to use your doorbell. Now the question is, do I need to come to your house to learn how to use your doorbell? I believe not! I just need to find the same doorbell in my environment and train with that. So, I found the same doorbell as yours in my environment, trained with it, and learned how to use it. Then I came to your house and used your doorbell, and you came to get the package, and my delivery was successful.

We can say the same about the interface of a contract. You can use any interface that has the same functions as the contract at the address to which you are sending a transaction to wrap the address of the contract to make a transaction. Hence, why we are using VRFCoordinatorV2_5Mock to wrap the address of a contract that is on the sepolia chain to make a transaction to the contract.

Please ask questions if anything is confusing.

[caodanbobo]

Hi @EngrPips, thanks for your reply.

The part I'm confused about is as follows: I understand that both the contracts VRFCoordinatorV2_5Mock and VRFCoordinatorV2_5 inherit the addConsumer function from SubscriptionAPI, and neither of them overrides this function. However, VRFCoordinatorV2_5Mock and VRFCoordinatorV2_5 are two different contracts with no inheritance relationship between them. When testing with the forked Sepolia network, we need an instance of VRFCoordinatorV2_5 instead of VRFCoordinatorV2_5Mock. Despite this, the code works fine without handling the logic for different networks.

[caodanbobo]

I asked ChatGPT this question, and here is the answer:

address vrfAdd = /* address of a deployed VRFCoordinatorV2_5 or VRFCoordinatorV2_5Mock */;
VRFCoordinatorV2_5Mock(vrfAdd).addConsumer(consumerAddress);
VRFCoordinatorV2_5(vrfAdd).addConsumer(consumerAddress);

In Solidity, both calls to addConsumer will behave the same way if the contract at vrfAdd correctly implements addConsumer.

To understand this clearly, i ask it a similar question: Assume foo is a virtual function in SubscriptionAPI, VRFCoordinatorV2_5 and VRFCoordinatorV2_5Mock provide their own implementations of foo, what would happen if VRFCoordinatorV2_5Mock(vrfAdd).foo() is called?

Answer:

1. In Solidity, casting an address to a contract type is essentially telling the compiler that you expect the contract at this address to conform to the interface of the specified type. It does not perform any runtime checks to verify that the contract at the address is actually of the specified type.
   Therefore, VRFCoordinatorV2_5Mock(vrfAdd) would not revert on its own. The cast simply tells the compiler to expect that the contract at vrfAdd implements the interface of VRFCoordinatorV2_5Mock.
2. The foo() function of VRFCoordinatorV2_5 (the actual contract at vrfAdd) will be executed, as Solidity determines the function to execute based on the actual deployed contract, not the cast type.

[EngrPips]

That is interesting. Thank you so much for putting this here. It helps us all learn more.