GUI2: cleaned up and improved up bind_status_label implementation

- Used constexpr if instead of SFINAE for the default getter functions
- Added support for menu buttons in the default getter function
- Fixes potentially calling get_value_label on classes derived from integer_selector other than slider
  (this function is a member of the slider class)
- Made value getters take a const reference (we don't want to be able to modify widgets here)
- Made value getters return a t_string (avoids conversion to std::string and set_label takes a t_string anyway)

src/gui/dialogs/editor/generator_settings.cpp

@@ -66,9 +66,9 @@ void generator_settings::pre_show(window& window)
 	// Do this *after* assigning the 'update_*_label_` functions or the game will crash!
 	adjust_minimum_size_by_players();
 
-	gui2::bind_status_label<slider>(&window, "villages", [](slider& s)->std::string { return formatter() << s.get_value() << _("/1000 tiles"); });
+	gui2::bind_status_label<slider>(&window, "villages", [](const slider& s) { return t_string(formatter() << s.get_value() << _("/1000 tiles")); });
 	gui2::bind_status_label<slider>(&window, "castle_size");
-	gui2::bind_status_label<slider>(&window, "landform", [](slider& s)->std::string {
+	gui2::bind_status_label<slider>(&window, "landform", [](const slider& s) {
 		return s.get_value() == 0 ? _("Inland") : (s.get_value() < max_coastal ? _("Coastal") : _("Island")); });
 }
 

src/gui/dialogs/preferences_dialog.cpp

@@ -670,9 +670,7 @@ void preferences_dialog::post_build(window& window)
 				connect_signal_notify_modified(menu,
 					std::bind([=](widget& w) { set(pref_name, option_ids[dynamic_cast<menu_button&>(w).get_value()]); }, std::placeholders::_1));
 
-				gui2::bind_status_label<menu_button>(main_grid, "setter", [](menu_button& m)->std::string {
-					return m.get_value_string();
-				}, "value");
+				gui2::bind_status_label<menu_button>(main_grid, "setter", default_status_value_getter<menu_button>, "value");
 
 				break;
 			}

src/gui/widgets/status_label_helper.hpp

@@ -15,7 +15,7 @@
 
 #include "gettext.hpp"
 #include "gui/core/event/dispatcher.hpp"
-#include "gui/widgets/integer_selector.hpp"
+#include "gui/widgets/menu_button.hpp"
 #include "gui/widgets/selectable_item.hpp"
 #include "gui/widgets/styled_widget.hpp"
 
@@ -23,24 +23,25 @@
 
 namespace gui2
 {
-/**
- * Default value getter for selectable widgets (like toggle buttons)
- */
 template<typename T>
-static inline std::enable_if_t<std::is_base_of_v<selectable_item, T>, std::string>
-default_status_value_getter(T& w)
+t_string default_status_value_getter(const T& w)
 {
-	return w.get_value_bool() ? _("yes") : _("no");
-}
+	// Menu Buttons
+	if constexpr(std::is_same_v<menu_button, T>) {
+		return w.get_value_string();
+	}
 
-/**
- * Default value getter for integer-based widgets (like sliders)
- */
-template<typename T>
-static inline std::enable_if_t<std::is_base_of_v<integer_selector, T>, std::string>
-default_status_value_getter(T& w)
-{
-	return w.get_value_label();
+	// Selectable widgets (like toggle buttons)
+	if constexpr(std::is_base_of_v<selectable_item, T>) {
+		return w.get_value_bool() ? _("yes") : _("no");
+	}
+
+	// Sliders
+	if constexpr(std::is_same_v<slider, T>) {
+		return w.get_value_label();
+	}
+
+	return w.get_label();
 }
 
 /**
@@ -63,7 +64,7 @@ template<typename W>
 std::function<void()> bind_status_label(
 		widget* find_in,
 		const std::string& source_id,
-		const std::function<std::string(W&)> value_getter = default_status_value_getter<W>,
+		const std::function<t_string(const W&)> value_getter = default_status_value_getter<W>,
 		const std::string& label_id = "")
 {
 	// If no label ID is provided, use the format source ID + '_label'.
@@ -76,9 +77,7 @@ std::function<void()> bind_status_label(
 	styled_widget& label = find_widget<styled_widget>(find_in, label_id_, false);
 
 	const auto update_label = [&, value_getter]() {
-		const std::string value = value_getter(source);
-
-		label.set_label(value);
+		label.set_label(value_getter(source));
 	};
 
 	// Bind the callback.