@0x/contracts-zero-ex: Address review comments.

contracts/zero-ex/contracts/src/transformers/FillQuoteTransformer.sol

@@ -35,6 +35,11 @@ import "./LibERC20Transformer.sol";
 contract FillQuoteTransformer is
     Transformer
 {
+    using LibERC20TokenV06 for IERC20TokenV06;
+    using LibERC20Transformer for IERC20TokenV06;
+    using LibSafeMathV06 for uint256;
+    using LibRichErrorsV06 for bytes;
+
     /// @dev Whether we are performing a market sell or buy.
     enum Side {
         Sell,
@@ -77,18 +82,15 @@ contract FillQuoteTransformer is
     }
 
     /// @dev The Exchange ERC20Proxy ID.
-    bytes4 constant private ERC20_ASSET_PROXY_ID = 0xf47261b0;
+    bytes4 private constant ERC20_ASSET_PROXY_ID = 0xf47261b0;
+    /// @dev Maximum uint256 value.
+    uint256 private constant MAX_UINT256 = uint256(-1);
 
     /// @dev The Exchange contract.
     IExchange public immutable exchange;
     /// @dev The ERC20Proxy address.
     address public immutable erc20Proxy;
 
-    using LibERC20TokenV06 for IERC20TokenV06;
-    using LibERC20Transformer for IERC20TokenV06;
-    using LibSafeMathV06 for uint256;
-    using LibRichErrorsV06 for bytes;
-
     /// @dev Create this contract.
     /// @param exchange_ The Exchange V3 instance.
     /// @param deploymentNonce_ The nonce of the deployer when deploying this contract.
@@ -132,7 +134,7 @@ contract FillQuoteTransformer is
             ).rrevert();
         }
 
-        if (data.side == Side.Sell && data.fillAmount == uint256(-1)) {
+        if (data.side == Side.Sell && data.fillAmount == MAX_UINT256) {
             // If `sellAmount == -1 then we are selling
             // the entire balance of `sellToken`. This is useful in cases where
             // the exact sell amount is not exactly known in advance, like when
@@ -181,7 +183,7 @@ contract FillQuoteTransformer is
                     data.fillAmount.safeSub(soldAmount).min256(
                         data.maxOrderFillAmounts.length > i
                         ? data.maxOrderFillAmounts[i]
-                        : uint256(-1)
+                        : MAX_UINT256
                     ),
                     singleProtocolFee
                 );
@@ -195,7 +197,7 @@ contract FillQuoteTransformer is
                     data.fillAmount.safeSub(boughtAmount).min256(
                         data.maxOrderFillAmounts.length > i
                         ? data.maxOrderFillAmounts[i]
-                        : uint256(-1)
+                        : MAX_UINT256
                     ),
                     singleProtocolFee
                 );

contracts/zero-ex/contracts/src/transformers/LibERC20Transformer.sol

@@ -25,11 +25,11 @@ import "@0x/contracts-erc20/contracts/src/v06/LibERC20TokenV06.sol";
 
 library LibERC20Transformer {
 
+    using LibERC20TokenV06 for IERC20TokenV06;
+
     /// @dev ETH pseudo-token address.
     address constant internal ETH_TOKEN_ADDRESS = 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;
 
-    using LibERC20TokenV06 for IERC20TokenV06;
-
     /// @dev Transfer ERC20 tokens and ETH.
     /// @param token An ERC20 or the ETH pseudo-token address (`ETH_TOKEN_ADDRESS`).
     /// @param to The recipient.

contracts/zero-ex/contracts/src/transformers/PayTakerTransformer.sol

@@ -33,6 +33,9 @@ contract PayTakerTransformer is
     Transformer
 {
     // solhint-disable no-empty-blocks
+    using LibRichErrorsV06 for bytes;
+    using LibSafeMathV06 for uint256;
+    using LibERC20Transformer for IERC20TokenV06;
 
     /// @dev Transform data to ABI-encode and pass into `transform()`.
     struct TransformData {
@@ -43,9 +46,8 @@ contract PayTakerTransformer is
         uint256[] amounts;
     }
 
-    using LibRichErrorsV06 for bytes;
-    using LibSafeMathV06 for uint256;
-    using LibERC20Transformer for IERC20TokenV06;
+    /// @dev Maximum uint256 value.
+    uint256 private constant MAX_UINT256 = uint256(-1);
 
     /// @dev Create this contract.
     /// @param deploymentNonce_ The nonce of the deployer when deploying this contract.
@@ -76,7 +78,7 @@ contract PayTakerTransformer is
             // The `amounts` array can be shorter than the `tokens` array.
             // Missing elements are treated as `uint256(-1)`.
             uint256 amount = data.amounts.length > i ? data.amounts[i] : uint256(-1);
-            if (amount == uint256(-1)) {
+            if (amount == MAX_UINT256) {
                 amount = data.tokens[i].getTokenBalanceOf(address(this));
             }
             if (amount != 0) {

contracts/zero-ex/contracts/src/transformers/WethTransformer.sol

@@ -31,6 +31,10 @@ import "./LibERC20Transformer.sol";
 contract WethTransformer is
     Transformer
 {
+    using LibRichErrorsV06 for bytes;
+    using LibSafeMathV06 for uint256;
+    using LibERC20Transformer for IERC20TokenV06;
+
     /// @dev Transform data to ABI-encode and pass into `transform()`.
     struct TransformData {
         // The token to wrap/unwrap. Must be either ETH or WETH.
@@ -42,10 +46,8 @@ contract WethTransformer is
 
     /// @dev The WETH contract address.
     IEtherTokenV06 public immutable weth;
-
-    using LibRichErrorsV06 for bytes;
-    using LibSafeMathV06 for uint256;
-    using LibERC20Transformer for IERC20TokenV06;
+    /// @dev Maximum uint256 value.
+    uint256 private constant MAX_UINT256 = uint256(-1);
 
     /// @dev Construct the transformer and store the WETH address in an immutable.
     /// @param weth_ The weth token.
@@ -80,7 +82,7 @@ contract WethTransformer is
         }
 
         uint256 amount = data.amount;
-        if (amount == uint256(-1)) {
+        if (amount == MAX_UINT256) {
             amount = data.token.getTokenBalanceOf(address(this));
         }