Solidity Advanced Guide: Creating New Contracts Within a Smart Contract

Introduction

On Ethereum, smart contracts can dynamically create new contracts, enabling complex decentralized applications like Uniswap's factory-generated liquidity pools. This guide explores contract creation using Solidity's create method, with practical examples from a simplified Uniswap V2 implementation.

Key Concepts: Contract Creation with create

How create Works

The create method deploys new contracts using the new keyword:

Contract x = new Contract{value: _value}(params)

• Contract: Target contract name
• x: Address of the deployed contract
• _value: Optional ETH transfer (for payable constructors)
• params: Constructor arguments

Factory Contract Pattern

Decentralized exchanges like Uniswap use factory contracts to:

1. Deploy multiple instances of template contracts (e.g., token pairs)
2. Manage contract addresses efficiently

Practical Implementation: Minimal Uniswap Clone

1. Pair Contract (Token Pair Manager)

contract Pair {
    address public factory; // Factory contract address
    address public token0; // First token
    address public token1; // Second token

    constructor() payable {
        factory = msg.sender;
    }

    function initialize(address _token0, address _token1) external {
        require(msg.sender == factory, 'Unauthorized');
        token0 = _token0;
        token1 = _token1;
    }
}

Key Features:

• Immutable factory address set during deployment
• initialize() configures token pairs post-creation

2. PairFactory Contract (Deployment Manager)

contract PairFactory {
    mapping(address => mapping(address => address)) public getPair;
    address[] public allPairs;

    function createPair(address tokenA, address tokenB) external returns (address pairAddr) {
        Pair pair = new Pair(); // Deploy new Pair contract
        pair.initialize(tokenA, tokenB);
        
        // Update address mappings
        pairAddr = address(pair);
        allPairs.push(pairAddr);
        getPair[tokenA][tokenB] = pairAddr;
        getPair[tokenB][tokenA] = pairAddr;
    }
}

Core Functions:

• Tracks all deployed pairs via allPairs array
• Enables O(1) address lookup with getPair mapping

👉 Explore advanced Solidity patterns for scalable DApp architectures.

Testing on Remix: Step-by-Step

1. Deploy PairFactory

2. Call createPair with:

   • WBNB: 0x2c44b726ADF1963cA47Af88B284C06f30380fC78
   • PEOPLE: 0xbb4CdB9CBd36B01bD1cBaEBF2De08d9173bc095c

3. Verify:

   • New Pair address generated (e.g., 0xD3e200...)
   • Token addresses stored correctly in Pair contract

Debug Tip: Use Remix's debugger to inspect the CREATE opcode execution.

FAQs

Q1: Why use factory contracts instead of direct deployment?

Factory contracts enable:

• Mass production of standardized contracts
• Centralized address management
• Gas efficiency through template reuse

Q2: Can created contracts create other contracts?

Yes! Contracts can recursively deploy others, but monitor gas limits and complexity.

Q3: How does create differ from create2?

create generates addresses unpredictably, while create2 allows deterministic address pre-calculation.

👉 Learn about gas optimization techniques for high-frequency contract deployments.

Best Practices

1. Access Control: Restrict initialize calls to factory contracts
2. Event Logging: Emit events for deployment tracking
3. Security Audits: Verify contract templates before mass deployment

This pattern powers DeFi ecosystems—master it to build scalable blockchain solutions.