Lesson 7: unit test - getpriceFeed()

[GaneshDonikena]

Hi all, I got a doubt a why we should use 'getPriceFeed()' instead of 'getPriceFeed'?. Why we should use parenthesis?.

'''
describe("constructor", function () {
it("sets the aggregator addresses correctly", async () => {
const response = await fundMe.getPriceFeed()
assert.equal(response, mockV3Aggregator.address)
})
})
'''

[alymurtazamemon]

@GaneshDonikena Because for all public variables, solidity generates by default a getter function. So when you call that outside of a contract, you call its getter function instead of the variable itself.

[alymurtazamemon]

@GaneshDonikena sorry My bad!

In your case, it is a private variable, and Patrick created a getter function for it, mentioned below that returns the AggregatorV3Interface instance.

AggregatorV3Interface private s_priceFeed;

function getPriceFeed() public view returns (AggregatorV3Interface) {
        return s_priceFeed;
}

[GaneshDonikena]

Thanks @ali-thegilfoyle but i think priceFeed is a contract by putting address into AggregatorV3Interface we preparing a contract, named it as 'priceFeed'. How can a contract become a function suddenly?

is priceFeed a function or contract?

[krakxn]

Firstly, why the parenthesis? It is because getPriceFeed() is a getter function in our FundMe contract to receive priceFeed. And functions always have () which signifies empty parameters.

Secondly, regarding interface, let me explain: AggregatorV3Interface is an interface (listed below), so, for you, the priceFeed is a type of interface. Hope this helped!

AggregatorV3Interface:

// SPDX-License-Identifier: MIT
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
    );
}

[GaneshDonikena]

@krakxn so you are saying priceFeed a getter function. I feel priceFeed is a AggregatorV3Interface copy just like object in python. I also believe interfaces are contracts with not fully functions just headings.

@ali-thegilfoyle

@PatrickAlphaC

[alymurtazamemon]

@ali-thegilfoyle I have answered above. Check that.

[krakxn]

@GaneshDonikena Please read again - in our FundMe contract: getPriceFeed() is a getter function which returns s_priceFeed; so, then in our script file, we firstly create a new variable called priceFeed (of type AggregatorV3Interface) when we create a fundMe contract, we call the getPriceFeed() and store what it returns in priceFeed, notice the difference!

And about interfaces, it is only viewed externally (keyword external is used for this) - and similar to abstract classes in OOP languages. Their purpose is to interact with other contracts

Hope this helped.