Uniswap pair = address(uint(keccak256(abi.encodePacked() Error

Question

I don't understand why i get this error when i try to compile my contract to swap tokens on different dex.

Here the Code:

//SPDX-License-Identifier: MIT

import "./Interfaces/IUniswapV2Router02.sol";
import "./Interfaces/IUniswapV2Factory.sol";
//import "./Interfaces/IUniswapV2Pair.sol";
import "./Interfaces/IERC20.sol";
import "./Interfaces/UniswapV2Library.sol";
//import "./Interfaces/IUniswapV2Callee.sol";


pragma solidity >0.5.0 < 0.9.0;

contract SwappingDex{

    address public constant uniswapRouter = 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D;
    address public constant uniswapFactory = 0x5C69bEe701ef814a2B6a3EDD4B1652CB9cc5aA6f;
    address public constant sushiSwapRouter = 0xd9e1cE17f2641f24aE83637ab66a2cca9C378B9F;
    address public constant sushiSwapFactory = 0xC0AEe478e3658e2610c5F7A4A2E1777cE9e4f2Ac;
    address public constant WETH = 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2;


    function swappingIn2DEX(address tokenIn, address tokenOut, uint amount, address to)external payable{

        address pairOnUniswap;
        address pairOnSushi;
        pairOnUniswap = IUniswapV2Factory(uniswapFactory).getPair(tokenIn, tokenOut);
        pairOnSushi = IUniswapV2Factory(sushiSwapFactory).getPair(tokenIn, tokenOut);

        require(
            pairOnSushi != 0x0000000000000000000000000000000000000000 &&
            pairOnUniswap != 0x0000000000000000000000000000000000000000,
            "No Pair"
        );

        address[] memory path;
        path = new address[](2);
        path[0] = tokenIn;
        path[1] = tokenOut;

        uint[]memory amountOutUniswap = IUniswapV2Router02(uniswapRouter).getAmountsOut(amount, path);


        IERC20(tokenIn).transferFrom(msg.sender, address(this), amount);
        IERC20(tokenIn).approve(uniswapRouter, amount);

        IUniswapV2Router02(uniswapRouter).swapETHForExactTokens{value: msg.value}(
            amountOutUniswap[1],
            path,
            to,
            block.timestamp
        );
}

hardhat.config.js


require("@nomiclabs/hardhat-waffle");
require("@nomiclabs/hardhat-ethers");
require("dotenv").config();


module.exports = {
  solidity: "0.8.4",

  networks: {
    hardhat: {
      forking:{
        url: "*******",
      },
    },
  }
};

Once i go for compile, via npx hardhat compile, i get this error :

TypeError: Explicit type conversion not allowed from "uint256" to "address". --> contracts/Interfaces/UniswapV2Library.sol:20:16: | 20 | pair = address(uint(keccak256(abi.encodePacked( | ^ (Relevant source part starts here and spans across multiple lines).

I was searching for some reason about it and i saw something talking about a cast for the address after the ^0.8.0 version. I already made projects on uniswap with same steps but is the first time i got this error. Can someone explain me why? Thanks a lot!

Did you know that there's a Stack site dedicated to Ethereum now? [Ethereum.se]. This, and your other question posted today, might be a better fit there. — Tangentially Perpendicular, Nov 12 '22 at 04:43

Yilmaz · Answer 1 · 2022-11-13T03:14:16.777

this is the UniswapV2Library.sol github repo. code complains about this

function pairFor(address factory, address tokenA, address tokenB) internal pure returns (address pair) {
        (address token0, address token1) = sortTokens(tokenA, tokenB);
        pair = address(uint(keccak256(abi.encodePacked(
                hex'ff',
                factory,
                keccak256(abi.encodePacked(token0, token1)),
                hex'96e8ac4277198ff8b6f785478aa9a39f403cb768dd02cbee326c3e7da348845f' // init code hash
            ))));
    }

You need to apply the settings of UNiswap repo. That repo is using ethereum-waffle.readthedocs and if you check the .waffle.json config in the root of project you see this settings:

{
  "compilerVersion": "./node_modules/solc",
  "outputType": "all",
  "compilerOptions": {
    "outputSelection": {
      "*": {
        "*": [
          "evm.bytecode.object",
          "evm.deployedBytecode.object",
          "abi",
          "evm.bytecode.sourceMap",
          "evm.deployedBytecode.sourceMap",
          "metadata"
        ],
        "": ["ast"]
      }
    },
    "evmVersion": "istanbul",
    "optimizer": {
      "enabled": true,
      "runs": 999999
    }
  }
}

I had a similar issue with UniswapV3 and I asked a question here and then answered. I use hardhat and I applied these settings from UniswapV3 repo.

const DEFAULT_COMPILER_SETTINGS = {
  version: '0.7.6',
  settings: {
    evmVersion: 'istanbul',
    optimizer: {
      enabled: true,
      runs: 1_000_000,
    },
    metadata: {
      bytecodeHash: 'none',
    },
  },
}

I think the main reason is using the evmVersion: 'istanbul',

If not try mutating pair. From here

pair = address(uint160(uint(keccak256(abi.encodePacked(
                hex'ff',
                factory,
                keccak256(abi.encodePacked(token0, token1)),
                hex'96e8ac4277198ff8b6f785478aa9a39f403cb768dd02cbee326c3e7da348845f' // init code hash
            )))));

thank you very much for yout answer....i tried to add your code in hardhat.config.js, but it doesn't work....I changed my contract version from 0.8.4 to 0.7.6 following example, but now i'm not able to use IERC20 Interface, SafeMath library and all the other interfaces... Now if i change to 0.8.4 version in your code and in my contract, i got same error of before....Is a casting problem using UniswapV2Library 100% like you said. Is different use IUniswapV2Router.getAmountsIn() ? — Matteo Gigli, Nov 12 '22 at 18:16
Finally. i got the result. I modified the UniswapV2Library.sol like you suggest. Thanks a lot Yilmaz. — Matteo Gigli, Nov 13 '22 at 09:48
Plains complaining as well....I just said a big thank you ,for your answer, when i understood how working with. — Matteo Gigli, Nov 14 '22 at 17:20

Uniswap pair = address(uint(keccak256(abi.encodePacked() Error

1 Answers1