Ethereum: Execution Reverted due to UniswapV2-Pair creation in constructor

As a new blockchain developer, it’s not uncommon to encounter issues when integrating external libraries and APIs into your smart contract. In this article, we’ll explore why adding a UniswapV2Pair creation inside the constructor of an Ethereum contract can cause execution errors.

What is Uniswap V2?

Uniswap V2 is a decentralized liquidity pool protocol that enables the swapping of cryptocurrencies on the Ethereum blockchain. It’s a popular choice for decentralized finance (DeFi) applications, and it’s widely used in various projects.

Why is it causing issues?

When you deploy an Ethereum contract with UniswapV2Pair creation inside its constructor, it can lead to two main problems:

• Execution Reverted: This error occurs when the contract attempts to execute a function call before setting up any dependencies or executing the underlying logic.

• Gas Overflow: The execution of UniswapV2Pair in the constructor can cause excessive gas usage, leading to higher transaction costs and potentially triggering withdrawal errors.

The Issue: UniswapV2-Pair creation inside constructor

In the Ethereum Solidity 0.8.x convention, it’s generally recommended to create a function that returns an instance of the UniswapV2Pair struct before executing any logic within its constructor. This approach ensures that all dependencies are set up correctly and avoids potential gas issues.

However, in some cases, you might need to use UniswapV2Pair directly inside the constructor. Unfortunately, Uniswap V2 does not provide a way to create an instance of UniswapV2Pair directly within its constructor. The UniswapV2Pair struct is not natively accessible from the contract’s code.

Workarounds and Solutions

To resolve this issue, you can consider the following alternatives:

• Create a separate function: Instead of using UniswapV2Pair directly inside the constructor, create a separate function that returns an instance of UniswapV2Pair. This way, you can control when the dependency is set up and avoid gas issues.

• Use external libraries: If possible, consider using external libraries that provide access to Uniswap V2 functionality, such as UniswapLib.

• Modify UniswapV2 implementation

  

  : You might be able to modify the Uniswap V2 implementation to create an instance of UniswapV2Pair directly within its constructor.

Conclusion

In conclusion, adding a UniswapV2Pair creation inside the constructor of an Ethereum contract can lead to execution errors due to gas issues and excessive gas usage. To resolve this issue, consider creating separate functions for setting up dependencies or using external libraries that provide access to Uniswap V2 functionality.

Remember to always test your smart contracts thoroughly before deploying them in production environments.

Example Code

To demonstrate the first workaround (creating a separate function), here’s an example code snippet:

pragma solidity ^0.8.0;


import "


contract UniswapV2 {

    constructor() public {

        // Create a separate function to set up the Uniswap V2 pair

        function createUniswapPair(address _path) internal returns (address, address) {

            // Set up the Uniswap V2 instance here

            UniswapV2 pair = new UniswapV2(_path);

            return (pair.address1, pair.address2);

        }


        // Use the separate function to create an instance of UniswapV2Pair

        address[] memory uniswapPath;

        (uniswapPath[0], uniswapPath[1]) = createUniswapPair("ethusd");

    }

}

Note that this is just a hypothetical example, and you should adapt it to your specific use case.

ETHEREUM IDENTIFIER _DISABLEINITIALIZERS