Adds EnumerableMap.

contracts/utils/EnumerableMap.sol

@@ -0,0 +1,83 @@
+library EnumerableMap {
+	struct Entry {
+		address key;
+		uint8 value;
+	}
+
+	struct Map {
+		mapping (address => uint256) index;
+		Entry[] entries;
+	}
+
+	// we initialize it with a placeholder item in the first position because we treat the array as 1-indexed since 0 is a special index (means no entry in the index)
+	function initialize(Map storage map) internal {
+		map.entries.push();
+	}
+
+	function contains(Map storage map, address key) internal view returns (bool) {
+		return map.index[key] != 0;
+	}
+
+	function add(Map storage map, address key, uint8 value) internal {
+		uint256 index = map.index[key];
+		if (index == 0) {
+			// create new entry
+			Entry memory entry = Entry({ key: key, value: value });
+			uint256 newEntryIndex = map.entries.length;
+			map.entries.push(entry);
+			map.index[key] = newEntryIndex;
+		} else {
+			// update existing entry
+			map.entries[map.index[key]].value = value;
+		}
+
+		require(map.entries[map.index[key]].key == key, "Key at inserted location does not match inserted key.");
+		require(map.entries[map.index[key]].value == value, "Value at inserted location does not match inserted value.");
+	}
+
+	function remove(Map storage map, address key) internal {
+		// get the index into entries array that this entry lives at
+		uint256 index = map.index[key];
+
+		// if this key doesn't exist in the index, then we have nothing to do
+		if (index == 0) return;
+
+		// if the entry we are removing isn't the last, overwrite it with the last entry
+		uint256 lastIndex = map.entries.length - 1;
+		if (index != lastIndex) {
+			Entry storage lastEntry = map.entries[lastIndex];
+			map.entries[index] = lastEntry;
+			map.index[lastEntry.key] = index;
+		}
+
+		// delete the last entry (if the item we are removing isn't last, it will have been overwritten inside the conditional above)
+		map.entries.pop();
+
+		// delete the index pointer
+		delete map.index[key];
+
+		require(map.index[key] == 0, "Removed key still exists in the index.");
+		require(map.entries[index].key != key, "Removed key still exists in the array at original index.");
+	}
+
+	function get(Map storage map, address key) internal view returns (uint8) {
+		uint256 index = map.index[key];
+		require(index != 0, "Provided key was not in the map.");
+		return map.entries[index].value;
+	}
+
+	function tryGet(Map storage map, address key) internal view returns (uint256) {
+		uint256 index = map.index[key];
+		if (index == 0) return 0;
+		return map.entries[index].value;
+	}
+
+	function enumerate(Map storage map) internal view returns (Entry[] memory) {
+		Entry[] memory output = new Entry[](map.entries.length - 1);
+
+		for (uint256 i = 1; i < map.entries.length; ++i) {
+			output[i - 1] = map.entries[i];
+		}
+		return output;
+	}
+}