run everything on constantinople

turn on compiler optimization

don't hardcode 18 decimals

add create2

name return values in factory

contracts/UniswapV2.sol

@@ -42,11 +42,10 @@ contract UniswapV2 is ERC20("Uniswap V2", "UNI-V2", 18, 0) {
         reentrancyLock = false;
     }
 
-    constructor(address _tokenA, address _tokenB) public {
-        require(address(_tokenA) != address(0) && _tokenB != address(0), "Uniswap: INVALID_ADDRESS");
+    constructor() public {
         factory = msg.sender;
-        tokenA = _tokenA;
-        tokenB = _tokenB;
+        // tokenA = _tokenA;
+        // tokenB = _tokenB;
     }
 
     function () external {}

contracts/UniswapV2Factory.sol

@@ -1,45 +1,62 @@
-// TODO review, create2
+// TODO create2 exchanges
 pragma solidity 0.5.12;
 
-import "./UniswapV2.sol";
+import "./interfaces/IUniswapV2Factory.sol";
 
-contract UniswapV2Factory {
-    event ExchangeCreated(address indexed token0, address indexed token1, address exchange);
+contract UniswapV2Factory is IUniswapV2Factory {
+    event ExchangeCreated(address indexed token0, address indexed token1, address exchange, uint256 exchangeCount);
 
-    mapping (address => address) internal exchangeToToken0;
-    mapping (address => address) internal exchangeToToken1;
-    mapping (address => mapping(address => address)) internal token0ToToken1ToExchange;
-
-    function orderTokens(address tokenA, address tokenB) internal pure returns (address, address) {
-        address token0 = tokenA < tokenB ? tokenA : tokenB;
-        address token1 = tokenA < tokenB ? tokenB : tokenA;
-        return (token0, token1);
+    struct Pair {
+        address token0;
+        address token1;
     }
 
-    function createExchange(address tokenA, address tokenB) public returns (address) {
-        require(tokenA != tokenB, "UniswapV2Factory: INVALID_PAIR");
-        require(tokenA != address(0) && tokenB != address(0), "UniswapV2Factory: NO_ZERO_ADDRESS_TOKENS");
+    bytes private exchangeBytecode;
+    uint256 public exchangeCount;
+    mapping (address => Pair) private exchangeToPair;
+    mapping (address => mapping(address => address)) private token0ToToken1ToExchange;
 
-        (address token0, address token1) = orderTokens(tokenA, tokenB);
-
-        require(token0ToToken1ToExchange[token0][token1] == address(0), "UniswapV2Factory: EXCHANGE_EXISTS");
-
-        UniswapV2 exchange = new UniswapV2(token0, token1);
-        exchangeToToken0[address(exchange)] = token0;
-        exchangeToToken1[address(exchange)] = token1;
-        token0ToToken1ToExchange[token0][token1] = address(exchange);
-
-        emit ExchangeCreated(token0, token1, address(exchange));
-
-        return address(exchange);
+    constructor(bytes memory _exchangeBytecode) public {
+        require(_exchangeBytecode.length >= 0x20, "UniswapV2Factory: SHORT_BYTECODE");
+        exchangeBytecode = _exchangeBytecode;
     }
 
-    function getExchange(address tokenA, address tokenB) public view returns (address) {
-        (address token0, address token1) = orderTokens(tokenA, tokenB);
-        return token0ToToken1ToExchange[token0][token1];
+    function orderTokens(address tokenA, address tokenB) private pure returns (Pair memory pair) {
+        pair = tokenA < tokenB ? Pair(tokenA, tokenB) : Pair(tokenB, tokenA);
     }
 
-    function getTokens(address exchange) public view returns (address, address) {
-        return (exchangeToToken0[exchange], exchangeToToken1[exchange]);
+    function getTokens(address exchange) public view returns (address token0, address token1) {
+        Pair storage pair = exchangeToPair[exchange];
+        (token0, token1) = (pair.token0, pair.token1);
+    }
+
+    function getExchange(address tokenA, address tokenB) public view returns (address exchange) {
+        Pair memory pair = orderTokens(tokenA, tokenB);
+        exchange = token0ToToken1ToExchange[pair.token0][pair.token1];
+    }
+
+    function createExchange(address tokenA, address tokenB) public returns (address exchange) {
+        require(tokenA != tokenB, "UniswapV2Factory: SAME_TOKEN");
+        require(tokenA != address(0) && tokenB != address(0), "UniswapV2Factory: ZERO_ADDRESS_TOKEN");
+
+        Pair memory pair = orderTokens(tokenA, tokenB);
+
+        require(token0ToToken1ToExchange[pair.token0][pair.token1] == address(0), "UniswapV2Factory: EXCHANGE_EXISTS");
+
+        bytes memory exchangeBytecodeMemory = exchangeBytecode;
+        uint256 exchangeBytecodeLength = exchangeBytecode.length;
+        bytes32 salt = keccak256(abi.encodePacked(pair.token0, pair.token1));
+        assembly {
+            exchange := create2(
+                0,
+                add(exchangeBytecodeMemory, 0x20),
+                exchangeBytecodeLength,
+                salt
+            )
+        }
+        exchangeToPair[exchange] = pair;
+        token0ToToken1ToExchange[pair.token0][pair.token1] = exchange;
+
+        emit ExchangeCreated(pair.token0, pair.token1, exchange, exchangeCount++);
     }
 }

contracts/interfaces/IERC20.sol

@@ -1,6 +1,9 @@
 pragma solidity 0.5.12;
 
 interface IERC20 {
+    event Transfer(address indexed from, address indexed to, uint256 value);
+    event Approval(address indexed owner, address indexed spender, uint256 value);
+
     function name() external view returns (string memory);
     function symbol() external view returns (string memory);
     function decimals() external view returns (uint8);
@@ -8,9 +11,6 @@ interface IERC20 {
     function balanceOf(address owner) external view returns (uint256);
     function allowance(address owner, address spender) external view returns (uint256);
 
-    event Transfer(address indexed from, address indexed to, uint256 value);
-    event Approval(address indexed owner, address indexed spender, uint256 value);
-
     function transfer(address to, uint256 value) external returns (bool);
     function transferFrom(address from, address to, uint256 value) external returns (bool);
     function burn(uint256 value) external;

contracts/interfaces/IUniswapV2Factory.sol

@@ -0,0 +1,11 @@
+pragma solidity 0.5.12;
+
+interface IUniswapV2Factory {
+    event ExchangeCreated(address indexed token0, address indexed token1, address exchange, uint256 exchangeNumber);
+
+    function exchangeCount() external view returns (uint256);
+    function getTokens(address exchange) external view returns (address token0, address token1);
+    function getExchange(address tokenA, address tokenB) external view returns (address exchange);
+
+    function createExchange(address tokenA, address tokenB) external returns (address exchange);
+}

test/ERC20.ts

@@ -4,7 +4,6 @@ import { Contract } from 'ethers'
 import { BigNumber, bigNumberify } from 'ethers/utils'
 
 import ERC20 from '../build/ERC20.json'
-import {} from 'ethers/utils'
 
 chai.use(solidity)
 const { expect } = chai
@@ -13,6 +12,7 @@ const decimalize = (n: number): BigNumber => bigNumberify(n).mul(bigNumberify(10
 
 const name = 'Mock ERC20'
 const symbol = 'MOCK'
+const decimals = 18
 const totalSupply = decimalize(1000)
 
 describe('ERC20', () => {
@@ -21,7 +21,7 @@ describe('ERC20', () => {
   let token: Contract
 
   beforeEach(async () => {
-    token = await deployContract(wallet, ERC20, [name, symbol, totalSupply])
+    token = await deployContract(wallet, ERC20, [name, symbol, decimals, totalSupply])
   })
 
   it('name, symbol, decimals, totalSupply, balanceOf', async () => {

test/UniswapV2Factory.ts

@@ -0,0 +1,54 @@
+import path from 'path'
+import chai from 'chai'
+import { solidity, createMockProvider, getWallets, deployContract } from 'ethereum-waffle'
+import { Contract } from 'ethers'
+import { keccak256, solidityPack, getAddress } from 'ethers/utils'
+
+import UniswapV2 from '../build/UniswapV2.json'
+import UniswapV2Factory from '../build/UniswapV2Factory.json'
+
+chai.use(solidity)
+const { expect } = chai
+
+const dummyTokens = ['0x1000000000000000000000000000000000000000', '0x2000000000000000000000000000000000000000']
+
+describe('UniswapV2Factory', () => {
+  const provider = createMockProvider(path.join(__dirname, '..', 'waffle.json'))
+  const [wallet] = getWallets(provider)
+  let bytecode: string
+  let factory: Contract
+
+  it('can deploy factory', async () => {
+    bytecode = `0x${UniswapV2.evm.bytecode.object}`
+
+    factory = await deployContract(wallet, UniswapV2Factory, [bytecode], {
+      gasLimit: (provider._web3Provider as any).options.gasLimit
+    })
+
+    expect(await factory.exchangeCount()).to.eq(0)
+  })
+
+  it('can create exchange', async () => {
+    const expectedAddress = getAddress(
+      `0x${keccak256(
+        [
+          '0xff',
+          factory.address.slice(2),
+          keccak256(solidityPack(['address', 'address'], dummyTokens)).slice(2),
+          keccak256(bytecode).slice(2)
+        ].join('')
+      ).slice(-40)}`
+    )
+
+    await expect(factory.createExchange(...dummyTokens))
+      .to.emit(factory, 'ExchangeCreated')
+      .withArgs(...[...dummyTokens, expectedAddress, 0])
+
+    expect(await factory.exchangeCount()).to.eq(1)
+    expect(await factory.getTokens(expectedAddress)).to.deep.eq(dummyTokens)
+    expect(await factory.getExchange(...dummyTokens)).to.eq(expectedAddress)
+
+    const exchange = new Contract(expectedAddress, UniswapV2.abi, provider)
+    expect(await exchange.factory()).to.eq(factory.address)
+  })
+})

waffle.json

@@ -1,3 +1,15 @@
 {
-  "solcVersion": "./node_modules/solc"
+  "solcVersion": "./node_modules/solc",
+  "compilerOptions": {
+    "evmVersion": "constantinople",
+    "optimizer": {
+      "enabled": true,
+      "runs": 1000
+    }
+  },
+  "ganacheOptions": {
+    "hardfork": "constantinople",
+    "mnemonic": "horn horn horn horn horn horn horn horn horn horn horn horn",
+    "gasLimit": "0x7A1200"
+  }
 }