Codechange: Switch DropDownList to directly use std::vector, thus making AutoDeleteSmallVector obsolete.

DropDownListItem are strongly managed using std::unique_ptr to ensure leak-free handling. Appropriate use
of move-semantics make intent a lot clearer than parameter comments and allows the compiler to generate
copy-free code for most situations.

2 files changed, 27 insertions, 37 deletions

diff --git a/src/widgets/dropdown.cpp b/src/widgets/dropdown.cpp
index d0ad6bc46..cb1382dd6 100644
--- a/src/widgets/dropdown.cpp
+++ b/src/widgets/dropdown.cpp
@@ -51,11 +51,11 @@ void DropDownListStringItem::Draw(int left, int right, int top, int bottom, bool
  * @return true if \a first precedes \a second.
  * @warning All items in the list need to be derivates of DropDownListStringItem.
  */
-/* static */ int DropDownListStringItem::NatSortFunc(const DropDownListItem * const *first, const DropDownListItem * const * second)
+/* static */ int DropDownListStringItem::NatSortFunc(std::unique_ptr<const DropDownListItem> const &first, std::unique_ptr<const DropDownListItem> const &second)
 {
 	char buffer1[512], buffer2[512];
-	GetString(buffer1, static_cast<const DropDownListStringItem*>(*first)->String(), lastof(buffer1));
-	GetString(buffer2, static_cast<const DropDownListStringItem*>(*second)->String(), lastof(buffer2));
+	GetString(buffer1, static_cast<const DropDownListStringItem*>(first.get())->String(), lastof(buffer1));
+	GetString(buffer2, static_cast<const DropDownListStringItem*>(second.get())->String(), lastof(buffer2));
 	return strnatcmp(buffer1, buffer2);
 }
 
@@ -126,7 +126,7 @@ struct DropdownWindow : Window {
 	WindowClass parent_wnd_class; ///< Parent window class.
 	WindowNumber parent_wnd_num;  ///< Parent window number.
 	int parent_button;            ///< Parent widget number where the window is dropped from.
-	const DropDownList *list;     ///< List with dropdown menu items.
+	const DropDownList list;      ///< List with dropdown menu items.
 	int selected_index;           ///< Index of the selected item in the list.
 	byte click_delay;             ///< Timer to delay selection.
 	bool drag_mode;
@@ -148,10 +148,10 @@ struct DropdownWindow : Window {
 	 * @param wi_colour     Colour of the parent widget.
 	 * @param scroll        Dropdown menu has a scrollbar.
 	 */
-	DropdownWindow(Window *parent, const DropDownList *list, int selected, int button, bool instant_close, const Point &position, const Dimension &size, Colours wi_colour, bool scroll)
-			: Window(&_dropdown_desc)
+	DropdownWindow(Window *parent, DropDownList &&list, int selected, int button, bool instant_close, const Point &position, const Dimension &size, Colours wi_colour, bool scroll)
+			: Window(&_dropdown_desc), list(std::move(list))
 	{
-		assert(list->size() > 0);
+		assert(this->list.size() > 0);
 
 		this->position = position;
 
@@ -174,18 +174,17 @@ struct DropdownWindow : Window {
 
 		/* Total length of list */
 		int list_height = 0;
-		for (const DropDownListItem *item : *list) {
+		for (const auto &item : this->list) {
 			list_height += item->Height(items_width);
 		}
 
 		/* Capacity is the average number of items visible */
-		this->vscroll->SetCapacity(size.height * (uint16)list->size() / list_height);
-		this->vscroll->SetCount((uint16)list->size());
+		this->vscroll->SetCapacity(size.height * (uint16)this->list.size() / list_height);
+		this->vscroll->SetCount((uint16)this->list.size());
 
 		this->parent_wnd_class = parent->window_class;
 		this->parent_wnd_num   = parent->window_number;
 		this->parent_button    = button;
-		this->list             = list;
 		this->selected_index   = selected;
 		this->click_delay      = 0;
 		this->drag_mode        = true;
@@ -207,7 +206,6 @@ struct DropdownWindow : Window {
 			pt.y -= w2->top;
 			w2->OnDropdownClose(pt, this->parent_button, this->selected_index, this->instant_close);
 		}
-		delete this->list;
 	}
 
 	virtual Point OnInitialPosition(int16 sm_width, int16 sm_height, int window_number)
@@ -229,7 +227,7 @@ struct DropdownWindow : Window {
 		int width = nwi->current_x - 4;
 		int pos   = this->vscroll->GetPosition();
 
-		for (const DropDownListItem *item : *this->list) {
+		for (const auto &item : this->list) {
 			/* Skip items that are scrolled up */
 			if (--pos >= 0) continue;
 
@@ -255,7 +253,7 @@ struct DropdownWindow : Window {
 
 		int y = r.top + 2;
 		int pos = this->vscroll->GetPosition();
-		for (const DropDownListItem *item : *this->list) {
+		for (const auto &item : this->list) {
 			int item_height = item->Height(r.right - r.left + 1);
 
 			/* Skip items that are scrolled up */
@@ -357,8 +355,7 @@ struct DropdownWindow : Window {
 /**
  * Show a drop down list.
  * @param w        Parent window for the list.
- * @param list     Prepopulated DropDownList. Will be deleted when the list is
- *                 closed.
+ * @param list     Prepopulated DropDownList.
  * @param selected The initially selected list item.
  * @param button   The widget which is passed to Window::OnDropdownSelect and OnDropdownClose.
  *                 Unless you override those functions, this should be then widget index of the dropdown button.
@@ -368,7 +365,7 @@ struct DropdownWindow : Window {
  * @param instant_close Set to true if releasing mouse button should close the
  *                      list regardless of where the cursor is.
  */
-void ShowDropDownListAt(Window *w, const DropDownList *list, int selected, int button, Rect wi_rect, Colours wi_colour, bool auto_width, bool instant_close)
+void ShowDropDownListAt(Window *w, DropDownList &&list, int selected, int button, Rect wi_rect, Colours wi_colour, bool auto_width, bool instant_close)
 {
 	DeleteWindowById(WC_DROPDOWN_MENU, 0);
 
@@ -384,7 +381,7 @@ void ShowDropDownListAt(Window *w, const DropDownList *list, int selected, int b
 	/* Total height of list */
 	uint height = 0;
 
-	for (const DropDownListItem *item : *list) {
+	for (const auto &item : list) {
 		height += item->Height(width);
 		if (auto_width) max_item_width = max(max_item_width, item->Width() + 5);
 	}
@@ -412,7 +409,7 @@ void ShowDropDownListAt(Window *w, const DropDownList *list, int selected, int b
 		/* If the dropdown doesn't fully fit, we need a dropdown. */
 		if (height > available_height) {
 			scroll = true;
-			uint avg_height = height / (uint)list->size();
+			uint avg_height = height / (uint)list.size();
 
 			/* Check at least there is space for one item. */
 			assert(available_height >= avg_height);
@@ -435,7 +432,7 @@ void ShowDropDownListAt(Window *w, const DropDownList *list, int selected, int b
 
 	Point dw_pos = { w->left + (_current_text_dir == TD_RTL ? wi_rect.right + 1 - (int)width : wi_rect.left), top};
 	Dimension dw_size = {width, height};
-	DropdownWindow *dropdown = new DropdownWindow(w, list, selected, button, instant_close, dw_pos, dw_size, wi_colour, scroll);
+	DropdownWindow *dropdown = new DropdownWindow(w, std::move(list), selected, button, instant_close, dw_pos, dw_size, wi_colour, scroll);
 
 	/* The dropdown starts scrolling downwards when opening it towards
 	 * the top and holding down the mouse button. It can be fooled by
@@ -446,8 +443,7 @@ void ShowDropDownListAt(Window *w, const DropDownList *list, int selected, int b
 /**
  * Show a drop down list.
  * @param w        Parent window for the list.
- * @param list     Prepopulated DropDownList. Will be deleted when the list is
- *                 closed.
+ * @param list     Prepopulated DropDownList.
  * @param selected The initially selected list item.
  * @param button   The widget within the parent window that is used to determine
  *                 the list's location.
@@ -456,7 +452,7 @@ void ShowDropDownListAt(Window *w, const DropDownList *list, int selected, int b
  * @param instant_close Set to true if releasing mouse button should close the
  *                      list regardless of where the cursor is.
  */
-void ShowDropDownList(Window *w, const DropDownList *list, int selected, int button, uint width, bool auto_width, bool instant_close)
+void ShowDropDownList(Window *w, DropDownList &&list, int selected, int button, uint width, bool auto_width, bool instant_close)
 {
 	/* Our parent's button widget is used to determine where to place the drop
 	 * down list window. */
@@ -483,7 +479,7 @@ void ShowDropDownList(Window *w, const DropDownList *list, int selected, int but
 		}
 	}
 
-	ShowDropDownListAt(w, list, selected, button, wi_rect, wi_colour, auto_width, instant_close);
+	ShowDropDownListAt(w, std::move(list), selected, button, wi_rect, wi_colour, auto_width, instant_close);
 }
 
 /**
@@ -499,21 +495,15 @@ void ShowDropDownList(Window *w, const DropDownList *list, int selected, int but
  */
 void ShowDropDownMenu(Window *w, const StringID *strings, int selected, int button, uint32 disabled_mask, uint32 hidden_mask, uint width)
 {
-	DropDownList *list = new DropDownList();
+	DropDownList list;
 
 	for (uint i = 0; strings[i] != INVALID_STRING_ID; i++) {
 		if (!HasBit(hidden_mask, i)) {
-			list->push_back(new DropDownListStringItem(strings[i], i, HasBit(disabled_mask, i)));
+			list.emplace_back(new DropDownListStringItem(strings[i], i, HasBit(disabled_mask, i)));
 		}
 	}
 
-	/* No entries in the list? */
-	if (list->size() == 0) {
-		delete list;
-		return;
-	}
-
-	ShowDropDownList(w, list, selected, button, width);
+	if (!list.empty()) ShowDropDownList(w, std::move(list), selected, button, width);
 }
 
 /**
diff --git a/src/widgets/dropdown_type.h b/src/widgets/dropdown_type.h
index bf8638a92..26c699f16 100644
--- a/src/widgets/dropdown_type.h
+++ b/src/widgets/dropdown_type.h
@@ -49,7 +49,7 @@ public:
 	void Draw(int left, int right, int top, int bottom, bool sel, Colours bg_colour) const override;
 	virtual StringID String() const { return this->string; }
 
-	static int CDECL NatSortFunc(const DropDownListItem * const *first, const DropDownListItem * const *second);
+	static int NatSortFunc(std::unique_ptr<const DropDownListItem> const &first, std::unique_ptr<const DropDownListItem> const &second);
 };
 
 /**
@@ -98,10 +98,10 @@ public:
 /**
  * A drop down list is a collection of drop down list items.
  */
-typedef AutoDeleteSmallVector<const DropDownListItem *> DropDownList;
+typedef std::vector<std::unique_ptr<const DropDownListItem>> DropDownList;
 
-void ShowDropDownListAt(Window *w, const DropDownList *list, int selected, int button, Rect wi_rect, Colours wi_colour, bool auto_width = false, bool instant_close = false);
+void ShowDropDownListAt(Window *w, DropDownList &&list, int selected, int button, Rect wi_rect, Colours wi_colour, bool auto_width = false, bool instant_close = false);
 
-void ShowDropDownList(Window *w, const DropDownList *list, int selected, int button, uint width = 0, bool auto_width = false, bool instant_close = false);
+void ShowDropDownList(Window *w, DropDownList &&list, int selected, int button, uint width = 0, bool auto_width = false, bool instant_close = false);
 
 #endif /* WIDGETS_DROPDOWN_TYPE_H */