add library TWStringSet (#331)

contracts/lib/TWStringSet.sol

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+// SPDX-License-Identifier: Apache 2.0
+// OpenZeppelin Contracts (last updated v4.7.0) (utils/structs/EnumerableSet.sol)
+
+pragma solidity ^0.8.0;
+
+library TWStringSet {
+    struct Set {
+        // Storage of set values
+        string[] _values;
+        // Position of the value in the `values` array, plus 1 because index 0
+        // means a value is not in the set.
+        mapping(string => uint256) _indexes;
+    }
+
+    /**
+     * @dev Add a value to a set. O(1).
+     *
+     * Returns true if the value was added to the set, that is if it was not
+     * already present.
+     */
+    function _add(Set storage set, string memory value) private returns (bool) {
+        if (!_contains(set, value)) {
+            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;
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    /**
+     * @dev Removes a value from a set. O(1).
+     *
+     * Returns true if the value was removed from the set, that is if it was
+     * present.
+     */
+    function _remove(Set storage set, string memory 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];
+
+        if (valueIndex != 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 lastIndex = set._values.length - 1;
+
+            if (lastIndex != toDeleteIndex) {
+                string memory 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
+            }
+
+            // Delete the slot where the moved value was stored
+            set._values.pop();
+
+            // Delete the index for the deleted slot
+            delete set._indexes[value];
+
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    /**
+     * @dev Returns true if the value is in the set. O(1).
+     */
+    function _contains(Set storage set, string memory value) private view returns (bool) {
+        return set._indexes[value] != 0;
+    }
+
+    /**
+     * @dev Returns the number of values on the set. O(1).
+     */
+    function _length(Set storage set) private view returns (uint256) {
+        return set._values.length;
+    }
+
+    /**
+     * @dev Returns the value stored at position `index` in the set. O(1).
+     *
+     * Note that there are no guarantees on the ordering of values inside the
+     * array, and it may change when more values are added or removed.
+     *
+     * Requirements:
+     *
+     * - `index` must be strictly less than {length}.
+     */
+    function _at(Set storage set, uint256 index) private view returns (string memory) {
+        return set._values[index];
+    }
+
+    /**
+     * @dev Return the entire set in an array
+     *
+     * WARNING: This operation will copy the entire storage to memory, which can be quite expensive. This is designed
+     * to mostly be used by view accessors that are queried without any gas fees. Developers should keep in mind that
+     * this function has an unbounded cost, and using it as part of a state-changing function may render the function
+     * uncallable if the set grows to a point where copying to memory consumes too much gas to fit in a block.
+     */
+    function _values(Set storage set) private view returns (string[] memory) {
+        return set._values;
+    }
+
+    /**
+     * @dev Add a value to a set. O(1).
+     *
+     * Returns true if the value was added to the set, that is if it was not
+     * already present.
+     */
+    function add(Set storage set, string memory value) internal returns (bool) {
+        return _add(set, value);
+    }
+
+    /**
+     * @dev Removes a value from a set. O(1).
+     *
+     * Returns true if the value was removed from the set, that is if it was
+     * present.
+     */
+    function remove(Set storage set, string memory value) internal returns (bool) {
+        return _remove(set, value);
+    }
+
+    /**
+     * @dev Returns true if the value is in the set. O(1).
+     */
+    function contains(Set storage set, string memory value) internal view returns (bool) {
+        return _contains(set, value);
+    }
+
+    /**
+     * @dev Returns the number of values in the set. O(1).
+     */
+    function length(Set storage set) internal view returns (uint256) {
+        return _length(set);
+    }
+
+    /**
+     * @dev Returns the value stored at position `index` in the set. O(1).
+     *
+     * Note that there are no guarantees on the ordering of values inside the
+     * array, and it may change when more values are added or removed.
+     *
+     * Requirements:
+     *
+     * - `index` must be strictly less than {length}.
+     */
+    function at(Set storage set, uint256 index) internal view returns (string memory) {
+        return _at(set, index);
+    }
+
+    /**
+     * @dev Return the entire set in an array
+     *
+     * WARNING: This operation will copy the entire storage to memory, which can be quite expensive. This is designed
+     * to mostly be used by view accessors that are queried without any gas fees. Developers should keep in mind that
+     * this function has an unbounded cost, and using it as part of a state-changing function may render the function
+     * uncallable if the set grows to a point where copying to memory consumes too much gas to fit in a block.
+     */
+    function values(Set storage set) internal view returns (string[] memory) {
+        return _values(set);
+    }
+}

docs/TWStringSet.md

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+# TWStringSet
+
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