From 1f5c9aa9e73b2d105739cae3d51bfb2ae5ef10c0 Mon Sep 17 00:00:00 2001
From: Noah Zinsmeister <noahwz@gmail.com>
Date: Fri, 24 Jan 2020 12:58:21 -0500
Subject: [PATCH] populate getExchange bidirectionally

---
 contracts/UniswapV2Factory.sol             | 33 +++++++++-------------
 contracts/interfaces/IUniswapV2Factory.sol |  8 ++++--
 2 files changed, 18 insertions(+), 23 deletions(-)

diff --git a/contracts/UniswapV2Factory.sol b/contracts/UniswapV2Factory.sol
index 204d96e..a391030 100644
--- a/contracts/UniswapV2Factory.sol
+++ b/contracts/UniswapV2Factory.sol
@@ -8,8 +8,8 @@ contract UniswapV2Factory is IUniswapV2Factory {
     address public feeTo;
     address public feeToSetter;
 
-    mapping(address => mapping(address => address)) private _getExchange;
-    address[] public exchanges;
+    mapping(address => mapping(address => address)) public getExchange;
+    address[] public allExchanges;
 
     event ExchangeCreated(address indexed token0, address indexed token1, address exchange, uint);
 
@@ -17,33 +17,26 @@ contract UniswapV2Factory is IUniswapV2Factory {
         feeToSetter = _feeToSetter;
     }
 
-    function sortTokens(address tokenA, address tokenB) public pure returns (address token0, address token1) {
-        require(tokenA != tokenB, 'UniswapV2: SAME_ADDRESS');
-        require(tokenA != address(0) && tokenB != address(0), 'UniswapV2: ZERO_ADDRESS');
-        (token0, token1) = tokenA < tokenB ? (tokenA, tokenB) : (tokenB, tokenA);
-    }
-
-    function getExchange(address tokenA, address tokenB) external view returns (address exchange) {
-        (address token0, address token1) = sortTokens(tokenA, tokenB);
-        exchange = _getExchange[token0][token1];
-    }
-
-    function exchangesCount() external view returns (uint) {
-        return exchanges.length;
+    function allExchangesLength() external view returns (uint) {
+        return allExchanges.length;
     }
 
     function createExchange(address tokenA, address tokenB) external returns (address exchange) {
-        (address token0, address token1) = sortTokens(tokenA, tokenB);
-        require(_getExchange[token0][token1] == address(0), 'UniswapV2: EXCHANGE_EXISTS');
+        require(tokenA != tokenB, 'UniswapV2: IDENTICAL_ADDRESSES');
+        (address token0, address token1) = tokenA < tokenB ? (tokenA, tokenB) : (tokenB, tokenA);
+        require(token0 != address(0), 'UniswapV2: ZERO_ADDRESS');
+        require(getExchange[token0][token1] == address(0), 'UniswapV2: EXCHANGE_EXISTS');
+        require(getExchange[token1][token0] == address(0), 'UniswapV2: EXCHANGE_EXISTS');
         bytes memory exchangeBytecode = type(UniswapV2Exchange).creationCode;
         bytes32 salt = keccak256(abi.encodePacked(token0, token1));
         assembly {
             exchange := create2(0, add(exchangeBytecode, 32), mload(exchangeBytecode), salt)
         }
         IUniswapV2Exchange(exchange).initialize(token0, token1);
-        _getExchange[token0][token1] = exchange;
-        exchanges.push(exchange);
-        emit ExchangeCreated(token0, token1, exchange, exchanges.length);
+        getExchange[token0][token1] = exchange;
+        getExchange[token1][token0] = exchange;
+        allExchanges.push(exchange);
+        emit ExchangeCreated(token0, token1, exchange, allExchanges.length);
     }
 
     function setFeeTo(address _feeTo) external {
diff --git a/contracts/interfaces/IUniswapV2Factory.sol b/contracts/interfaces/IUniswapV2Factory.sol
index 15e9b83..453f635 100644
--- a/contracts/interfaces/IUniswapV2Factory.sol
+++ b/contracts/interfaces/IUniswapV2Factory.sol
@@ -6,10 +6,12 @@ interface IUniswapV2Factory {
     function feeTo() external view returns (address);
     function feeToSetter() external view returns (address);
 
-    function sortTokens(address tokenA, address tokenB) external pure returns (address token0, address token1);
     function getExchange(address tokenA, address tokenB) external view returns (address exchange);
-    function exchanges(uint) external view returns (address exchange);
-    function exchangesCount() external view returns (uint);
+    function allExchanges(uint) external view returns (address exchange);
+    function allExchangesLength() external view returns (uint);
 
     function createExchange(address tokenA, address tokenB) external returns (address exchange);
+
+    function setFeeTo(address) external;
+    function setFeeToSetter(address) external;    
 }