dropdown: accept impl Into<Cow<'_, str>

This allows using `format!` in the `view` function rather than
having to store all strings in the model
which is in theory less efficient but it's also much less likely to lead to stale data.

src/widget/dropdown/mod.rs

@@ -4,6 +4,8 @@
 
 //! Displays a list of options in a popover menu on select.
 
+use std::borrow::Cow;
+
 pub mod menu;
 use iced_core::window;
 pub use menu::Menu;
@@ -17,14 +19,15 @@ use crate::surface;
 
 /// Displays a list of options in a popover menu on select.
 pub fn dropdown<
+    'a,
     S: AsRef<str> + std::clone::Clone + Send + Sync + 'static,
     Message: 'static + Clone,
 >(
-    selections: &[S],
+    selections: impl Into<Cow<'a, [S]>>,
     selected: Option<usize>,
     on_selected: impl Fn(usize) -> Message + Send + Sync + 'static,
-) -> Dropdown<'_, S, Message, Message> {
+) -> Dropdown<'a, S, Message, Message> {
-    Dropdown::new(selections, selected, on_selected)
+    Dropdown::new(selections.into(), selected, on_selected)
 }
 
 /// Displays a list of options in a popover menu on select.
@@ -35,7 +38,7 @@ pub fn popup_dropdown<
     Message: 'static + Clone,
     AppMessage: 'static + Clone,
 >(
-    selections: &'a [S],
+    selections: impl Into<Cow<'a, [S]>>,
     selected: Option<usize>,
     on_selected: impl Fn(usize) -> Message + Send + Sync + 'static,
     _parent_id: window::Id,
@@ -43,7 +46,7 @@ pub fn popup_dropdown<
     _map_action: impl Fn(Message) -> AppMessage + Send + Sync + 'static,
 ) -> Dropdown<'a, S, Message, AppMessage> {
     let dropdown: Dropdown<'_, S, Message, AppMessage> =
-        Dropdown::new(selections, selected, on_selected);
+        Dropdown::new(selections.into(), selected, on_selected);
 
     #[cfg(all(feature = "winit", feature = "wayland"))]
     let dropdown = dropdown.with_popup(_parent_id, _on_surface_action, _map_action);

src/widget/dropdown/widget.rs

@@ -34,9 +34,9 @@ where
     #[setters(skip)]
     on_selected: Arc<dyn Fn(usize) -> Message + Send + Sync>,
     #[setters(skip)]
-    selections: &'a [S],
+    selections: Cow<'a, [S]>,
     #[setters]
-    icons: &'a [icon::Handle],
+    icons: Cow<'a, [icon::Handle]>,
     #[setters(skip)]
     selected: Option<usize>,
     #[setters(into)]
@@ -73,14 +73,14 @@ where
     /// Creates a new [`Dropdown`] with the given list of selections, the current
     /// selected value, and the message to produce when an option is selected.
     pub fn new(
-        selections: &'a [S],
+        selections: Cow<'a, [S]>,
         selected: Option<usize>,
         on_selected: impl Fn(usize) -> Message + 'static + Send + Sync,
     ) -> Self {
         Self {
             on_selected: Arc::new(on_selected),
             selections,
-            icons: &[],
+            icons: Cow::Borrowed(&[]),
             selected,
             width: Length::Shrink,
             gap: Self::DEFAULT_GAP,
@@ -246,12 +246,12 @@ where
             self.positioner.clone(),
             self.on_selected.clone(),
             self.selected,
-            self.selections,
+            &self.selections,
             || tree.state.downcast_mut::<State>(),
             self.window_id,
             self.on_surface_action.clone(),
             self.action_map.clone(),
-            self.icons,
+            &self.icons,
             self.gap,
             self.padding,
             self.text_size,
@@ -322,8 +322,8 @@ where
             self.text_size.unwrap_or(14.0),
             self.text_line_height,
             self.font,
-            self.selections,
+            &self.selections,
-            self.icons,
+            &self.icons,
             self.selected,
             self.on_selected.as_ref(),
             translation,