Lesson 4: Library - DeclarationError: Undeclared identifier. How should we call a function from library that doesn't require parameter?

[nsawit]

I added a function (function getEthPrice()) that doesn't accept parameter in PriceConverter library. How should we use it in other contract?

library PriceConverter{
    function getEthPrice() public view returns (uint256){
        AggregatorV3Interface priceFeed = AggregatorV3Interface(0x8A753747A1Fa494EC906cE90E9f37563A8AF630e);
        (,int256 price,,,) = priceFeed.latestRoundData();
        return uint256(price * 1e10);
    }


    function getUSDPrice(uint256 ethAmount) public view returns(uint256){
        uint256 ethPrice = getEthPrice();
        uint256 ethUSD = (ethPrice * ethAmount) / 1e18;
        return ethUSD;
    }
}

FundMe.sol

    function fund() public payable{
        require(msg.value.getUSDPrice() >= minimumUSD, "Insufficient amount mo!"); 
        senders[msg.sender] = msg.value.getUSDPrice(); // this one works fine
        getEthPrice(); // This error would be thrown DeclarationError: Undeclared identifier.
    }

[krakxn]

The following should fix it:

function fund() public payable{
        require(msg.value.getUSDPrice() >= minimumUSD, "Insufficient amount mo!"); 
        senders[msg.sender] = msg.value.getUSDPrice(); // this one works fine
- getEthPrice(); // This error would be thrown DeclarationError: Undeclared identifier.       
+ uint256 ethPrice = getEthPrice();   
    }

[nsawit]

@krakxn
It throws "DeclarationError: Undeclared identifier.
--> contracts/FundMe.sol:33:28:
|
33 | uint256 ethPrice = getEthPrice();
| ^^^^^^^^^^^"

PriceConverter.sol

import "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";

library PriceConverter{
    function getEthPrice() public view returns (uint256){
        AggregatorV3Interface priceFeed = AggregatorV3Interface(0x8A753747A1Fa494EC906cE90E9f37563A8AF630e);
        (,int256 price,,,) = priceFeed.latestRoundData();
        return uint256(price * 1e10);
    }

    function getUSDPrice(uint256 ethAmount) public view returns(uint256){
        uint256 ethPrice = getEthPrice();
        uint256 ethUSD = (ethPrice * ethAmount) / 1e18;
        return ethUSD;
        //
    }
}

FundMe.sol

//SPDX-License-Identifier: MIT

pragma solidity ^0.8.8;

import "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";
import "./PriceConverter.sol";

contract FundMe{
    using PriceConverter for uint256;

    uint256 public nValue;
    uint256 public constant minimumUSD = 10 * 1e18;
    
    address[] public funders;
    mapping(address => uint256) public sender;

    address public owner;


    constructor(){
        owner = msg.sender;
    }

    function fund() public payable{
        //want to set minimum fund amount in USD
        // Sending ETH to this contract
        require(msg.value.getUSDPrice() >= minimumUSD, "Insufficient amount mo!"); // 1e18 == 1* 10 ** 18 == 1000000000000000000
        funders.push(msg.sender);
        sender[msg.sender] = getUSD(msg.value);//msg.value.getUSDPrice();
    }

    function getUSD(uint256 ethAmount) public view returns(uint256){
        uint256 ethPrice = getEthPrice(); // this would throw DeclarationError: Undeclared identifier.
        uint256 ethUSD = (ethPrice * ethAmount) / 1e18;
        return ethUSD;
    }

[alymurtazamemon]

@nsawit You can call it like this

PriceConverter.getEthPrice();

[nsawit]

this one worked! Thanks