Lesson 4: AggregatorV3Interface

[viganzeqiri]

Hey there, I have a question. In lesson 4 I saw Patrick imported the code for the interface of AggregatorV3Interface into remix, but I am not sure how did it work, how did remix know were to get the logic for getting the version, that interface could be some-other interface I wrote, we didnt import anything from chainlink. Hope I am clear with my question

[alymurtazamemon]

@viganzeqiri

when we imported that import "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol"; it automatically gets the ABI of the contract while compiling.

[maikelowen]

As far as I understand you can either copy and paste the code from the chainlink example, as Patrick does initially, or import it as already mentioned.

[viganzeqiri]

Hey Miguel, but what if I had some open source contract and I implemented a similar interface, how does it know which ones logic to use?

[maikelowen]

I am not sure I understand your question, but as far as I know the common way to use an external smart contract would be importing it as Ali said. You can import as many contracts as you want. Then, when you are implementing the function, you will refer by its name to the one you need in that case

[viganzeqiri]

not sure if I am explaining this good, will try it again.

Patrick copied this interface below to the FundMe contract

pragma solidity ^0.8.0;

interface AggregatorV3Interface {
  function decimals() external view returns (uint8);

  function description() external view returns (string memory);

  function version() external view returns (uint256);

  // getRoundData and latestRoundData should both raise "No data present"
  // if they do not have data to report, instead of returning unset values
  // which could be misinterpreted as actual reported values.
  function getRoundData(uint80 _roundId)
    external
    view
    returns (
      uint80 roundId,
      int256 answer,
      uint256 startedAt,
      uint256 updatedAt,
      uint80 answeredInRound
    );

  function latestRoundData()
    external
    view
    returns (
      uint80 roundId,
      int256 answer,
      uint256 startedAt,
      uint256 updatedAt,
      uint80 answeredInRound
    );
}

and he used the version function to get the version.

What If I had a similar interface in some other personal repo with different logic for version function
e.g.

pragma solidity ^0.8.0;

interface AggregatorV3Interface {
  function decimals() external view returns (uint8);

  function description() external view returns (string memory);

  function version() external view returns (int256);

  // getRoundData and latestRoundData should both raise "No data present"
  // if they do not have data to report, instead of returning unset values
  // which could be misinterpreted as actual reported values.
  function getRoundData(uint80 _roundId)
    external
    view
    returns (
      uint80 roundId,
      int256 answer,
      uint256 startedAt,
      uint256 updatedAt,
      uint80 answeredInRound
    );

  function latestRoundData()
    external
    view
    returns (
      uint80 roundId,
      int256 answer,
      uint256 startedAt,
      uint256 updatedAt,
      uint80 answeredInRound
    );
} 

I am not sure how does Solidity knew where to get the logic of that Interface, we never imported anything we just pasted the copied code?

Hope I am clear now

[alymurtazamemon]

@viganzeqiri

There are three ways you can use Contract and when compiling, ABI automatically will be created.

1. You can place the contract code in the same folder where your main contract is placed, by doing this you do not need to import anything and solidity will know that you are referring to this contract.
2. You can place the contract in another file, and import it into the file where your main contract is placed.
3. You can directly import the contract interface without placing the contract into a file or in the same contract file.

with all these ways, the solidity will know which contract you are referring to.

If you have a similar contract, you can use it with any of the three above ways.

And suppose you are importing two contracts with similar names then you need to give an alias with the imports to distinguish between them.

hope it clears your query.

[mattjaf]

interface(address) equals the deployed contract.