Rename internal variables in EnumerableSet for improved readability (#4577)

Co-authored-by: Francisco Giordano <fg@frang.io>

contracts/utils/structs/EnumerableSet.sol

@@ -51,9 +51,9 @@ library EnumerableSet {
     struct Set {
         // Storage of set values
         bytes32[] _values;
-        // Position of the value in the `values` array, plus 1 because index 0
-        // means a value is not in the set.
-        mapping(bytes32 value => uint256) _indexes;
+        // Position is the index of the value in the `values` array plus 1.
+        // Position 0 is used to mean a value is not in the set.
+        mapping(bytes32 value => uint256) _positions;
     }
 
     /**
@@ -67,7 +67,7 @@ library EnumerableSet {
             set._values.push(value);
             // The value is stored at length-1, but we add 1 to all indexes
             // and use 0 as a sentinel value
-            set._indexes[value] = set._values.length;
+            set._positions[value] = set._values.length;
             return true;
         } else {
             return false;
@@ -81,32 +81,32 @@ library EnumerableSet {
      * present.
      */
     function _remove(Set storage set, bytes32 value) private returns (bool) {
-        // We read and store the value's index to prevent multiple reads from the same storage slot
-        uint256 valueIndex = set._indexes[value];
+        // We cache the value's position to prevent multiple reads from the same storage slot
+        uint256 position = set._positions[value];
 
-        if (valueIndex != 0) {
+        if (position != 0) {
             // Equivalent to contains(set, value)
             // To delete an element from the _values array in O(1), we swap the element to delete with the last one in
             // the array, and then remove the last element (sometimes called as 'swap and pop').
             // This modifies the order of the array, as noted in {at}.
 
-            uint256 toDeleteIndex = valueIndex - 1;
+            uint256 valueIndex = position - 1;
             uint256 lastIndex = set._values.length - 1;
 
-            if (lastIndex != toDeleteIndex) {
+            if (valueIndex != lastIndex) {
                 bytes32 lastValue = set._values[lastIndex];
 
-                // Move the last value to the index where the value to delete is
-                set._values[toDeleteIndex] = lastValue;
-                // Update the index for the moved value
-                set._indexes[lastValue] = valueIndex; // Replace lastValue's index to valueIndex
+                // Move the lastValue to the index where the value to delete is
+                set._values[valueIndex] = lastValue;
+                // Update the tracked position of the lastValue (that was just moved)
+                set._positions[lastValue] = position;
             }
 
             // Delete the slot where the moved value was stored
             set._values.pop();
 
-            // Delete the index for the deleted slot
-            delete set._indexes[value];
+            // Delete the tracked position for the deleted slot
+            delete set._positions[value];
 
             return true;
         } else {
@@ -118,7 +118,7 @@ library EnumerableSet {
      * @dev Returns true if the value is in the set. O(1).
      */
     function _contains(Set storage set, bytes32 value) private view returns (bool) {
-        return set._indexes[value] != 0;
+        return set._positions[value] != 0;
     }
 
     /**

scripts/generate/templates/EnumerableSet.js

@@ -61,9 +61,9 @@ const defaultSet = () => `\
 struct Set {
     // Storage of set values
     bytes32[] _values;
-    // Position of the value in the \`values\` array, plus 1 because index 0
-    // means a value is not in the set.
-    mapping(bytes32 value => uint256) _indexes;
+    // Position is the index of the value in the \`values\` array plus 1.
+    // Position 0 is used to mean a value is not in the set.
+    mapping(bytes32 value => uint256) _positions;
 }
 
 /**
@@ -77,7 +77,7 @@ function _add(Set storage set, bytes32 value) private returns (bool) {
         set._values.push(value);
         // The value is stored at length-1, but we add 1 to all indexes
         // and use 0 as a sentinel value
-        set._indexes[value] = set._values.length;
+        set._positions[value] = set._values.length;
         return true;
     } else {
         return false;
@@ -91,32 +91,32 @@ function _add(Set storage set, bytes32 value) private returns (bool) {
  * present.
  */
 function _remove(Set storage set, bytes32 value) private returns (bool) {
-    // We read and store the value's index to prevent multiple reads from the same storage slot
-    uint256 valueIndex = set._indexes[value];
+    // We cache the value's position to prevent multiple reads from the same storage slot
+    uint256 position = set._positions[value];
 
-    if (valueIndex != 0) {
+    if (position != 0) {
         // Equivalent to contains(set, value)
         // To delete an element from the _values array in O(1), we swap the element to delete with the last one in
         // the array, and then remove the last element (sometimes called as 'swap and pop').
         // This modifies the order of the array, as noted in {at}.
 
-        uint256 toDeleteIndex = valueIndex - 1;
+        uint256 valueIndex = position - 1;
         uint256 lastIndex = set._values.length - 1;
 
-        if (lastIndex != toDeleteIndex) {
+        if (valueIndex != lastIndex) {
             bytes32 lastValue = set._values[lastIndex];
 
-            // Move the last value to the index where the value to delete is
-            set._values[toDeleteIndex] = lastValue;
-            // Update the index for the moved value
-            set._indexes[lastValue] = valueIndex; // Replace lastValue's index to valueIndex
+            // Move the lastValue to the index where the value to delete is
+            set._values[valueIndex] = lastValue;
+            // Update the tracked position of the lastValue (that was just moved)
+            set._positions[lastValue] = position;
         }
 
         // Delete the slot where the moved value was stored
         set._values.pop();
 
-        // Delete the index for the deleted slot
-        delete set._indexes[value];
+        // Delete the tracked position for the deleted slot
+        delete set._positions[value];
 
         return true;
     } else {
@@ -128,7 +128,7 @@ function _remove(Set storage set, bytes32 value) private returns (bool) {
  * @dev Returns true if the value is in the set. O(1).
  */
 function _contains(Set storage set, bytes32 value) private view returns (bool) {
-    return set._indexes[value] != 0;
+    return set._positions[value] != 0;
 }
 
 /**