Use `std::variant` in `StringOrView`

We also add a direct string move-assignment (`operator=(std::string &&)`),
which results in better codegen.

As a consequence, we have to replace `= {}` assignments with `= StringOrView {}`
because `= {}` is now ambiguous.

Source/control.cpp

@@ -883,7 +883,7 @@ void InitControlPan()
 	for (bool &buttonEnabled : chrbtn)
 		buttonEnabled = false;
 	chrbtnactive = false;
-	InfoString = {};
+	InfoString = StringOrView {};
 	RedrawComponent(PanelDrawComponent::Health);
 	RedrawComponent(PanelDrawComponent::Mana);
 	CloseCharPanel();
@@ -1165,7 +1165,7 @@ void DrawInfoBox(const Surface &out)
 {
 	DrawPanelBox(out, { 177, 62, 288, 63 }, GetMainPanel().position + Displacement { 177, 46 });
 	if (!panelflag && !trigflag && pcursinvitem == -1 && pcursstashitem == StashStruct::EmptyCell && !spselflag) {
-		InfoString = {};
+		InfoString = StringOrView {};
 		InfoColor = UiFlags::ColorWhite;
 	}
 	Player &myPlayer = *MyPlayer;

Source/controls/plrctrls.cpp

@@ -1781,7 +1781,7 @@ void plrctrls_after_check_curs_move()
 		return;
 	}
 	if (!invflag) {
-		InfoString = {};
+		InfoString = StringOrView {};
 		FindActor();
 		FindItemOrObject();
 		FindTrigger();

Source/diablo.cpp

@@ -1435,7 +1435,7 @@ void TimeoutCursor(bool bTimeout)
 		if (sgnTimeoutCurs == CURSOR_NONE && sgbMouseDown == CLICK_NONE) {
 			sgnTimeoutCurs = pcurs;
 			multi_net_ping();
-			InfoString = {};
+			InfoString = StringOrView {};
 			AddPanelString(_("-- Network timeout --"));
 			AddPanelString(_("-- Waiting for players --"));
 			NewCursor(CURSOR_HOURGLASS);
@@ -1449,7 +1449,7 @@ void TimeoutCursor(bool bTimeout)
 		if (pcurs == CURSOR_HOURGLASS)
 			NewCursor(sgnTimeoutCurs);
 		sgnTimeoutCurs = CURSOR_NONE;
-		InfoString = {};
+		InfoString = StringOrView {};
 		RedrawEverything();
 	}
 }
@@ -1459,7 +1459,7 @@ void HelpKeyPressed()
 	if (HelpFlag) {
 		HelpFlag = false;
 	} else if (stextflag != TalkID::None) {
-		InfoString = {};
+		InfoString = StringOrView {};
 		AddPanelString(_("No help available")); /// BUGFIX: message isn't displayed
 		AddPanelString(_("while in stores"));
 		LastMouseButtonAction = MouseActionType::None;

Source/panels/spell_list.cpp

@@ -114,7 +114,7 @@ void DrawSpell(const Surface &out)
 
 void DrawSpellList(const Surface &out)
 {
-	InfoString = {};
+	InfoString = StringOrView {};
 
 	Player &myPlayer = *MyPlayer;
 

Source/utils/string_or_view.hpp

@@ -3,78 +3,51 @@
 #include <string>
 #include <string_view>
 #include <utility>
+#include <variant>
 
 namespace devilution {
 
 class StringOrView {
 public:
 	StringOrView()
-	    : owned_(false)
+	    : rep_ { std::string_view {} }
-	    , view_()
 	{
 	}
 
+	StringOrView(StringOrView &&) noexcept = default;
+
 	StringOrView(std::string &&str)
-	    : owned_(true)
+	    : rep_ { std::move(str) }
-	    , str_(std::move(str))
 	{
 	}
 
 	StringOrView(std::string_view str)
-	    : owned_(false)
+	    : rep_ { str }
-	    , view_(str)
 	{
 	}
 
-	StringOrView(StringOrView &&other) noexcept
+	StringOrView &operator=(StringOrView &&) noexcept = default;
-	    : owned_(other.owned_)
-	{
-		if (other.owned_) {
-			new (&str_) std::string(std::move(other.str_));
-		} else {
-			new (&view_) std::string_view(other.view_);
-		}
-	}
 
-	StringOrView &operator=(StringOrView &&other) noexcept
+	StringOrView &operator=(std::string &&value) noexcept
 	{
-		if (owned_) {
+		rep_ = std::move(value);
-			if (other.owned_) {
-				str_ = std::move(other.str_);
-			} else {
-				str_.~basic_string();
-				owned_ = false;
-				new (&view_) std::string_view(other.view_);
-			}
-		} else {
-			if (other.owned_) {
-				view_.~basic_string_view();
-				owned_ = true;
-				new (&str_) std::string(std::move(other.str_));
-			} else {
-				view_ = other.view_;
-			}
-		}
 		return *this;
 	}
 
-	~StringOrView()
+	StringOrView &operator=(std::string_view value) noexcept
 	{
-		if (owned_) {
+		rep_ = value;
-			str_.~basic_string();
+		return *this;
-		} else {
-			view_.~basic_string_view();
-		}
 	}
 
 	bool empty() const
 	{
-		return owned_ ? str_.empty() : view_.empty();
+		return std::visit([](auto &&val) -> bool { return val.empty(); }, rep_);
 	}
 
 	std::string_view str() const
 	{
-		return owned_ ? str_ : view_;
+		return std::visit([](auto &&val) -> std::string_view { return val; }, rep_);
 	}
 
 	operator std::string_view() const
@@ -83,11 +56,7 @@ public:
 	}
 
 private:
-	bool owned_;
+	std::variant<std::string, std::string_view> rep_;
-	union {
-		std::string str_;
-		std::string_view view_;
-	};
 };
 
 } // namespace devilution