Implement Range Iterators

This PR implements range iterators in the base containers (Vector, Map, List, Pair Set).
Given several of these data structures will be replaced by more efficient versions, having a common iterator API will make this simpler.
Iterating can be done as follows (examples):

```C++
//Vector<String>
for(const String& I: vector) {

}
//List<String>
for(const String& I: list) {

}
//Map<String,int>
for(const KeyValue<String,int>&I : map) {
	print_line("key: "+I.key+" value: "+itos(I.value));

}

//if intending to write the elements, reference can be used

//Map<String,int>
for(KeyValue<String,int>& I: map) {
	I.value = 25;
	//this will fail because key is always const
	//I.key = "hello"
}

```

The containers are (for now) not STL compatible, since this would mean changing how they work internally (STL uses a special head/tail allocation for end(), while Godot Map/Set/List do not).
The idea is to change the Godot versions to be more compatible with STL, but this will happen after conversion to new iterators have taken place.

6 files changed, 373 insertions, 24 deletions

diff --git a/core/templates/list.h b/core/templates/list.h
index 010e35eed8..6047b89670 100644
--- a/core/templates/list.h
+++ b/core/templates/list.h
@@ -135,6 +135,83 @@ public:
 		_FORCE_INLINE_ Element() {}
 	};
 
+	typedef T ValueType;
+
+	struct Iterator {
+		_FORCE_INLINE_ T &operator*() const {
+			return E->get();
+		}
+		_FORCE_INLINE_ T *operator->() const { return &E->get(); }
+		_FORCE_INLINE_ Iterator &operator++() {
+			E = E->next();
+			return *this;
+		}
+		_FORCE_INLINE_ Iterator &operator--() {
+			E = E->prev();
+			return *this;
+		}
+
+		_FORCE_INLINE_ bool operator==(const Iterator &b) const { return E == b.E; }
+		_FORCE_INLINE_ bool operator!=(const Iterator &b) const { return E != b.E; }
+
+		Iterator(Element *p_E) { E = p_E; }
+		Iterator() {}
+		Iterator(const Iterator &p_it) { E = p_it.E; }
+
+	private:
+		Element *E = nullptr;
+	};
+
+	struct ConstIterator {
+		_FORCE_INLINE_ const T &operator*() const {
+			return E->get();
+		}
+		_FORCE_INLINE_ const T *operator->() const { return &E->get(); }
+		_FORCE_INLINE_ ConstIterator &operator++() {
+			E = E->next();
+			return *this;
+		}
+		_FORCE_INLINE_ ConstIterator &operator--() {
+			E = E->prev();
+			return *this;
+		}
+
+		_FORCE_INLINE_ bool operator==(const Iterator &b) const { return E == b.E; }
+		_FORCE_INLINE_ bool operator!=(const Iterator &b) const { return E != b.E; }
+
+		_FORCE_INLINE_ ConstIterator(const Element *p_E) { E = p_E; }
+		_FORCE_INLINE_ ConstIterator() {}
+		_FORCE_INLINE_ ConstIterator(const ConstIterator &p_it) { E = p_it.E; }
+
+	private:
+		const Element *E = nullptr;
+	};
+
+	_FORCE_INLINE_ Iterator begin() {
+		return Iterator(front());
+	}
+	_FORCE_INLINE_ Iterator end() {
+		return Iterator(nullptr);
+	}
+
+#if 0
+	//to use when replacing find()
+	_FORCE_INLINE_ Iterator find(const K &p_key) {
+		return Iterator(find(p_key));
+	}
+#endif
+	_FORCE_INLINE_ ConstIterator begin() const {
+		return ConstIterator(front());
+	}
+	_FORCE_INLINE_ ConstIterator end() const {
+		return ConstIterator(nullptr);
+	}
+#if 0
+	//to use when replacing find()
+	_FORCE_INLINE_ ConstIterator find(const K &p_key) const {
+		return ConstIterator(find(p_key));
+	}
+#endif
 private:
 	struct _Data {
 		Element *first = nullptr;
diff --git a/core/templates/map.h b/core/templates/map.h
index 7dfee13d2c..a47547d355 100644
--- a/core/templates/map.h
+++ b/core/templates/map.h
@@ -33,6 +33,7 @@
 
 #include "core/error/error_macros.h"
 #include "core/os/memory.h"
+#include "core/templates/pair.h"
 
 // based on the very nice implementation of rb-trees by:
 // https://web.archive.org/web/20120507164830/http://web.mit.edu/~emin/www/source_code/red_black_tree/index.html
@@ -55,11 +56,12 @@ public:
 		Element *parent = nullptr;
 		Element *_next = nullptr;
 		Element *_prev = nullptr;
-		K _key;
-		V _value;
-		//_Data *data;
+		KeyValue<K, V> _data;
 
 	public:
+		KeyValue<K, V> &key_value() { return _data; }
+		const KeyValue<K, V> &key_value() const { return _data; }
+
 		const Element *next() const {
 			return _next;
 		}
@@ -73,23 +75,106 @@ public:
 			return _prev;
 		}
 		const K &key() const {
-			return _key;
+			return _data.key;
 		}
 		V &value() {
-			return _value;
+			return _data.value;
 		}
 		const V &value() const {
-			return _value;
+			return _data.value;
 		}
 		V &get() {
-			return _value;
+			return _data.value;
 		}
 		const V &get() const {
-			return _value;
+			return _data.value;
 		}
-		Element() {}
+		Element(const KeyValue<K, V> &p_data) :
+				_data(p_data) {}
 	};
 
+	typedef KeyValue<K, V> ValueType;
+
+	struct Iterator {
+		_FORCE_INLINE_ KeyValue<K, V> &operator*() const {
+			return E->key_value();
+		}
+		_FORCE_INLINE_ KeyValue<K, V> *operator->() const { return &E->key_value(); }
+		_FORCE_INLINE_ Iterator &operator++() {
+			E = E->next();
+			return *this;
+		}
+		_FORCE_INLINE_ Iterator &operator--() {
+			E = E->prev();
+			return *this;
+		}
+
+		_FORCE_INLINE_ bool operator==(const Iterator &b) const { return E == b.E; }
+		_FORCE_INLINE_ bool operator!=(const Iterator &b) const { return E != b.E; }
+
+		Iterator(Element *p_E) { E = p_E; }
+		Iterator() {}
+		Iterator(const Iterator &p_it) { E = p_it.E; }
+
+	private:
+		Element *E = nullptr;
+	};
+
+	struct ConstIterator {
+		_FORCE_INLINE_ const KeyValue<K, V> &operator*() const {
+			return E->key_value();
+		}
+		_FORCE_INLINE_ const KeyValue<K, V> *operator->() const { return &E->key_value(); }
+		_FORCE_INLINE_ ConstIterator &operator++() {
+			E = E->next();
+			return *this;
+		}
+		_FORCE_INLINE_ ConstIterator &operator--() {
+			E = E->prev();
+			return *this;
+		}
+
+		_FORCE_INLINE_ bool operator==(const ConstIterator &b) const { return E == b.E; }
+		_FORCE_INLINE_ bool operator!=(const ConstIterator &b) const { return E != b.E; }
+
+		ConstIterator(const Element *p_E) { E = p_E; }
+		ConstIterator() {}
+		ConstIterator(const ConstIterator &p_it) { E = p_it.E; }
+
+	private:
+		const Element *E = nullptr;
+	};
+
+	_FORCE_INLINE_ Iterator begin() {
+		return Iterator(front());
+	}
+	_FORCE_INLINE_ Iterator end() {
+		return Iterator(nullptr);
+	}
+
+#if 0
+	//to use when replacing find()
+	_FORCE_INLINE_ Iterator find(const K &p_key) {
+		return Iterator(find(p_key));
+	}
+#endif
+	_FORCE_INLINE_ void remove(const Iterator &p_iter) {
+		return erase(p_iter.E);
+	}
+
+	_FORCE_INLINE_ ConstIterator begin() const {
+		return ConstIterator(front());
+	}
+	_FORCE_INLINE_ ConstIterator end() const {
+		return ConstIterator(nullptr);
+	}
+
+#if 0
+	//to use when replacing find()
+	_FORCE_INLINE_ ConstIterator find(const K &p_key) const {
+		return ConstIterator(find(p_key));
+	}
+#endif
 private:
 	struct _Data {
 		Element *_root = nullptr;
@@ -107,7 +192,7 @@ private:
 		}
 
 		void _create_root() {
-			_root = memnew_allocator(Element, A);
+			_root = memnew_allocator(Element(KeyValue<K, V>(K(), V())), A);
 			_root->parent = _root->left = _root->right = _nil;
 			_root->color = BLACK;
 		}
@@ -216,9 +301,9 @@ private:
 		C less;
 
 		while (node != _data._nil) {
-			if (less(p_key, node->_key)) {
+			if (less(p_key, node->_data.key)) {
 				node = node->left;
-			} else if (less(node->_key, p_key)) {
+			} else if (less(node->_data.key, p_key)) {
 				node = node->right;
 			} else {
 				return node; // found
@@ -236,9 +321,9 @@ private:
 		while (node != _data._nil) {
 			prev = node;
 
-			if (less(p_key, node->_key)) {
+			if (less(p_key, node->_data.key)) {
 				node = node->left;
-			} else if (less(node->_key, p_key)) {
+			} else if (less(node->_data.key, p_key)) {
 				node = node->right;
 			} else {
 				return node; // found
@@ -249,7 +334,7 @@ private:
 			return nullptr; // tree empty
 		}
 
-		if (less(p_key, prev->_key)) {
+		if (less(p_key, prev->_data.key)) {
 			prev = prev->_prev;
 		}
 
@@ -312,25 +397,25 @@ private:
 		while (node != _data._nil) {
 			new_parent = node;
 
-			if (less(p_key, node->_key)) {
+			if (less(p_key, node->_data.key)) {
 				node = node->left;
-			} else if (less(node->_key, p_key)) {
+			} else if (less(node->_data.key, p_key)) {
 				node = node->right;
 			} else {
-				node->_value = p_value;
+				node->_data.value = p_value;
 				return node; // Return existing node with new value
 			}
 		}
 
-		Element *new_node = memnew_allocator(Element, A);
+		typedef KeyValue<K, V> KV;
+		Element *new_node = memnew_allocator(Element(KV(p_key, p_value)), A);
 		new_node->parent = new_parent;
 		new_node->right = _data._nil;
 		new_node->left = _data._nil;
-		new_node->_key = p_key;
-		new_node->_value = p_value;
+
 		//new_node->data=_data;
 
-		if (new_parent == _data._root || less(p_key, new_parent->_key)) {
+		if (new_parent == _data._root || less(p_key, new_parent->_data.key)) {
 			new_parent->left = new_node;
 		} else {
 			new_parent->right = new_node;
@@ -575,7 +660,7 @@ public:
 		CRASH_COND(!_data._root);
 		const Element *e = find(p_key);
 		CRASH_COND(!e);
-		return e->_value;
+		return e->_data.value;
 	}
 
 	V &operator[](const K &p_key) {
@@ -588,7 +673,7 @@ public:
 			e = insert(p_key, V());
 		}
 
-		return e->_value;
+		return e->_data.value;
 	}
 
 	Element *front() const {
diff --git a/core/templates/pair.h b/core/templates/pair.h
index bc1a764694..31706b6ecb 100644
--- a/core/templates/pair.h
+++ b/core/templates/pair.h
@@ -31,6 +31,8 @@
 #ifndef PAIR_H
 #define PAIR_H
 
+#include "core/typedefs.h"
+
 template <class F, class S>
 struct Pair {
 	F first;
@@ -64,4 +66,37 @@ struct PairSort {
 	}
 };
 
+template <class K, class V>
+struct KeyValue {
+	const K key;
+	V value;
+
+	void operator=(const KeyValue &p_kv) = delete;
+	_FORCE_INLINE_ KeyValue(const KeyValue &p_kv) :
+			key(p_kv.key),
+			value(p_kv.value) {
+	}
+	_FORCE_INLINE_ KeyValue(const K &p_key, const V &p_value) :
+			key(p_key),
+			value(p_value) {
+	}
+};
+
+template <class K, class V>
+bool operator==(const KeyValue<K, V> &pair, const KeyValue<K, V> &other) {
+	return (pair.key == other.key) && (pair.value == other.value);
+}
+
+template <class K, class V>
+bool operator!=(const KeyValue<K, V> &pair, const KeyValue<K, V> &other) {
+	return (pair.key != other.key) || (pair.value != other.value);
+}
+
+template <class K, class V>
+struct KeyValueSort {
+	bool operator()(const KeyValue<K, V> &A, const KeyValue<K, V> &B) const {
+		return A.key < B.key;
+	}
+};
+
 #endif // PAIR_H
diff --git a/core/templates/set.h b/core/templates/set.h
index 3036ecf27d..245c174862 100644
--- a/core/templates/set.h
+++ b/core/templates/set.h
@@ -77,6 +77,85 @@ public:
 		Element() {}
 	};
 
+	typedef T ValueType;
+
+	struct Iterator {
+		_FORCE_INLINE_ T &operator*() const {
+			return E->get();
+		}
+		_FORCE_INLINE_ T *operator->() const { return &E->get(); }
+		_FORCE_INLINE_ Iterator &operator++() {
+			E = E->next();
+			return *this;
+		}
+		_FORCE_INLINE_ Iterator &operator--() {
+			E = E->prev();
+			return *this;
+		}
+
+		_FORCE_INLINE_ bool operator==(const Iterator &b) const { return E == b.E; }
+		_FORCE_INLINE_ bool operator!=(const Iterator &b) const { return E != b.E; }
+
+		Iterator(Element *p_E) { E = p_E; }
+		Iterator() {}
+		Iterator(const Iterator &p_it) { E = p_it.E; }
+
+	private:
+		Element *E = nullptr;
+	};
+
+	struct ConstIterator {
+		_FORCE_INLINE_ const T &operator*() const {
+			return E->get();
+		}
+		_FORCE_INLINE_ const T *operator->() const { return &E->get(); }
+		_FORCE_INLINE_ ConstIterator &operator++() {
+			E = E->next();
+			return *this;
+		}
+		_FORCE_INLINE_ ConstIterator &operator--() {
+			E = E->prev();
+			return *this;
+		}
+
+		_FORCE_INLINE_ bool operator==(const Iterator &b) const { return E == b.E; }
+		_FORCE_INLINE_ bool operator!=(const Iterator &b) const { return E != b.E; }
+
+		_FORCE_INLINE_ ConstIterator(const Element *p_E) { E = p_E; }
+		_FORCE_INLINE_ ConstIterator() {}
+		_FORCE_INLINE_ ConstIterator(const ConstIterator &p_it) { E = p_it.E; }
+
+	private:
+		const Element *E = nullptr;
+	};
+
+	_FORCE_INLINE_ Iterator begin() {
+		return Iterator(front());
+	}
+	_FORCE_INLINE_ Iterator end() {
+		return Iterator(nullptr);
+	}
+
+#if 0
+	//to use when replacing find()
+	_FORCE_INLINE_ Iterator find(const K &p_key) {
+		return Iterator(find(p_key));
+	}
+#endif
+
+	_FORCE_INLINE_ ConstIterator begin() const {
+		return ConstIterator(front());
+	}
+	_FORCE_INLINE_ ConstIterator end() const {
+		return ConstIterator(nullptr);
+	}
+
+#if 0
+	//to use when replacing find()
+	_FORCE_INLINE_ ConstIterator find(const K &p_key) const {
+		return ConstIterator(find(p_key));
+	}
+#endif
 private:
 	struct _Data {
 		Element *_root = nullptr;
diff --git a/core/templates/vector.h b/core/templates/vector.h
index dae8874a87..08cbef6ba4 100644
--- a/core/templates/vector.h
+++ b/core/templates/vector.h
@@ -187,6 +187,70 @@ public:
 		return false;
 	}
 
+	struct Iterator {
+		_FORCE_INLINE_ T &operator*() const {
+			return *elem_ptr;
+		}
+		_FORCE_INLINE_ T *operator->() const { return elem_ptr; }
+		_FORCE_INLINE_ Iterator &operator++() {
+			elem_ptr++;
+			return *this;
+		}
+		_FORCE_INLINE_ Iterator &operator--() {
+			elem_ptr--;
+			return *this;
+		}
+
+		_FORCE_INLINE_ bool operator==(const Iterator &b) const { return elem_ptr == b.elem_ptr; }
+		_FORCE_INLINE_ bool operator!=(const Iterator &b) const { return elem_ptr != b.elem_ptr; }
+
+		Iterator(T *p_ptr) { elem_ptr = p_ptr; }
+		Iterator() {}
+		Iterator(const Iterator &p_it) { elem_ptr = p_it.elem_ptr; }
+
+	private:
+		T *elem_ptr = nullptr;
+	};
+
+	struct ConstIterator {
+		_FORCE_INLINE_ const T &operator*() const {
+			return *elem_ptr;
+		}
+		_FORCE_INLINE_ const T *operator->() const { return elem_ptr; }
+		_FORCE_INLINE_ ConstIterator &operator++() {
+			elem_ptr++;
+			return *this;
+		}
+		_FORCE_INLINE_ ConstIterator &operator--() {
+			elem_ptr--;
+			return *this;
+		}
+
+		_FORCE_INLINE_ bool operator==(const ConstIterator &b) const { return elem_ptr == b.elem_ptr; }
+		_FORCE_INLINE_ bool operator!=(const ConstIterator &b) const { return elem_ptr != b.elem_ptr; }
+
+		ConstIterator(T *p_ptr) { elem_ptr = p_ptr; }
+		ConstIterator() {}
+		ConstIterator(const ConstIterator &p_it) { elem_ptr = p_it.elem_ptr; }
+
+	private:
+		const T *elem_ptr = nullptr;
+	};
+
+	_FORCE_INLINE_ Iterator begin() {
+		return Iterator(ptrw());
+	}
+	_FORCE_INLINE_ Iterator end() {
+		return Iterator(ptrw() + size());
+	}
+
+	_FORCE_INLINE_ ConstIterator begin() const {
+		return ConstIterator(ptr());
+	}
+	_FORCE_INLINE_ ConstIterator end() const {
+		return ConstIterator(ptr() + size());
+	}
+
 	_FORCE_INLINE_ Vector() {}
 	_FORCE_INLINE_ Vector(const Vector &p_from) { _cowdata._ref(p_from._cowdata); }
 
diff --git a/editor/audio_stream_preview.h b/editor/audio_stream_preview.h
index 61567598ed..9cf47fd51a 100644
--- a/editor/audio_stream_preview.h
+++ b/editor/audio_stream_preview.h
@@ -75,6 +75,15 @@ class AudioStreamPreviewGenerator : public Node {
 			thread = p_rhs.thread;
 			return *this;
 		}
+		Preview(const Preview &p_rhs) {
+			preview = p_rhs.preview;
+			base_stream = p_rhs.base_stream;
+			playback = p_rhs.playback;
+			generating.set_to(generating.is_set());
+			id = p_rhs.id;
+			thread = p_rhs.thread;
+		}
+		Preview() {}
 	};
 
 	Map<ObjectID, Preview> previews;