List container improvements and testing

- support range based for loops
 - add remove() method to remove a node
 - add clear() to empty entire list and delete nodes
 - add empty() helper

src/include/containers/List.hpp

@@ -1,6 +1,6 @@
 /****************************************************************************
  *
- *   Copyright (C) 2012 PX4 Development Team. All rights reserved.
+ *   Copyright (C) 2012-2019 PX4 Development Team. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -34,11 +34,13 @@
 /**
  * @file List.hpp
  *
- * A linked list.
+ * An intrusive linked list.
  */
 
 #pragma once
 
+#include <stdlib.h>
+
 template<class T>
 class ListNode
 {
@@ -64,8 +66,88 @@ public:
 		_head = newNode;
 	}
 
+	bool remove(T removeNode)
+	{
+		// base case
+		if (removeNode == _head) {
+			_head = nullptr;
+			return true;
+		}
+
+		for (T node = getHead(); node != nullptr; node = node->getSibling()) {
+			// is sibling the node to remove?
+			if (node->getSibling() == removeNode) {
+				// replace sibling
+				if (node->getSibling() != nullptr) {
+					node->setSibling(node->getSibling()->getSibling());
+
+				} else {
+					node->setSibling(nullptr);
+				}
+
+				return true;
+			}
+		}
+
+		return false;
+	}
+
+	struct Iterator {
+		T node;
+		Iterator(T v) : node(v) {}
+
+		operator T() const { return node; }
+		operator T &() { return node; }
+		T operator* () const { return node; }
+		Iterator &operator++ ()
+		{
+			if (node) {
+				node = node->getSibling();
+			};
+
+			return *this;
+		}
+	};
+
+	Iterator begin() { return Iterator(getHead()); }
+	Iterator end() { return Iterator(nullptr); }
+
 	const T getHead() const { return _head; }
 
+	bool empty() const { return getHead() == nullptr; }
+
+	size_t size() const
+	{
+		size_t sz = 0;
+
+		for (auto node = getHead(); node != nullptr; node = node->getSibling()) {
+			sz++;
+		}
+
+		return sz;
+	}
+
+	void deleteNode(T node)
+	{
+		if (remove(node)) {
+			// only delete if node was successfully removed
+			delete node;
+		}
+	}
+
+	void clear()
+	{
+		auto node = getHead();
+
+		while (node != nullptr) {
+			auto next = node->getSibling();
+			delete node;
+			node = next;
+		}
+
+		_head = nullptr;
+	}
+
 protected:
 
 	T _head{nullptr};