# Uniswap v2 factory

By [web3zoom](https://paragraph.com/@web3zoom) · 2025-08-02

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看了uniswap v2 很多遍，对于其中代码的熟悉程度在慢慢提高，因此做了些笔记来记录其中的要点：

factory合约的作用：

*   创建代币对createPair：
    
    通过使用salt方式，通过create2方法对生成代币对地址，同时还初始化了代币对合约。
    
*   对代币对进行排序：
    
    (address token0, address token1) = tokenA < tokenB ? (tokenA, tokenB) : (tokenB, tokenA);
    
    **这样做的好处**：
    
    1、保证交易对的一致性，并避免某些错误（例如：同一对代币不同的排序会导致流动性池地址不同，进而导致交易失败或价格错误）。
    
    2、防止潜在攻击，比如：重入攻击
    
    3、流动性池子管理，可能会影响交易价格和滑点
    
    4、价格计算，避免不必要的价格波动
    

    pragma solidity =0.5.16;
    
    import './interfaces/IUniswapV2Factory.sol';
    import './UniswapV2Pair.sol';
    
    contract UniswapV2Factory is IUniswapV2Factory {
        address public feeTo;
        address public feeToSetter;
    
        mapping(address => mapping(address => address)) public getPair;
        address[] public allPairs;
    
        event PairCreated(address indexed token0, address indexed token1, address pair, uint);
    
        constructor(address _feeToSetter) public {
            feeToSetter = _feeToSetter;
        }
    
        function allPairsLength() external view returns (uint) {
            return allPairs.length;
        }
    
        function createPair(address tokenA, address tokenB) external returns (address pair) {
            require(tokenA != tokenB, 'UniswapV2: IDENTICAL_ADDRESSES');
            (address token0, address token1) = tokenA < tokenB ? (tokenA, tokenB) : (tokenB, tokenA);
            require(token0 != address(0), 'UniswapV2: ZERO_ADDRESS');
            require(getPair[token0][token1] == address(0), 'UniswapV2: PAIR_EXISTS'); // single check is sufficient
            bytes memory bytecode = type(UniswapV2Pair).creationCode;
            bytes32 salt = keccak256(abi.encodePacked(token0, token1));
            assembly {
                pair := create2(0, add(bytecode, 32), mload(bytecode), salt)
            }
            IUniswapV2Pair(pair).initialize(token0, token1);
            getPair[token0][token1] = pair;
            getPair[token1][token0] = pair; // populate mapping in the reverse direction
            allPairs.push(pair);
            emit PairCreated(token0, token1, pair, allPairs.length);
        }
    
        function setFeeTo(address _feeTo) external {
            require(msg.sender == feeToSetter, 'UniswapV2: FORBIDDEN');
            feeTo = _feeTo;
        }
    
        function setFeeToSetter(address _feeToSetter) external {
            require(msg.sender == feeToSetter, 'UniswapV2: FORBIDDEN');
            feeToSetter = _feeToSetter;
        }
    }

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*Originally published on [web3zoom](https://paragraph.com/@web3zoom/uniswap-v2-factory)*