Introduce `Tag` and `State` opaque types in `iced_pure::widget::tree`

16 files changed, 101 insertions, 197 deletions

diff --git a/pure/src/widget.rs b/pure/src/widget.rs
index 9112dd9a..03b668d3 100644
--- a/pure/src/widget.rs
+++ b/pure/src/widget.rs
@@ -37,15 +37,7 @@ use iced_native::mouse;
 use iced_native::renderer;
 use iced_native::{Clipboard, Hasher, Length, Point, Rectangle, Shell};
 
-use std::any::{self, Any};
-
 pub trait Widget<Message, Renderer> {
-    fn tag(&self) -> any::TypeId;
-
-    fn state(&self) -> Box<dyn Any>;
-
-    fn children_state(&self) -> Vec<Tree>;
-
     fn width(&self) -> Length;
 
     fn height(&self) -> Length;
@@ -68,6 +60,18 @@ pub trait Widget<Message, Renderer> {
         viewport: &Rectangle,
     );
 
+    fn tag(&self) -> tree::Tag {
+        tree::Tag::stateless()
+    }
+
+    fn state(&self) -> tree::State {
+        tree::State::None
+    }
+
+    fn children(&self) -> Vec<Tree> {
+        Vec::new()
+    }
+
     fn diff(&self, _tree: &mut Tree) {}
 
     fn mouse_interaction(
diff --git a/pure/src/widget/button.rs b/pure/src/widget/button.rs
index 6dc1016c..55cbf8b4 100644
--- a/pure/src/widget/button.rs
+++ b/pure/src/widget/button.rs
@@ -1,4 +1,5 @@
-use crate::widget::{Element, Tree, Widget};
+use crate::widget::tree::{self, Tree};
+use crate::widget::{Element, Widget};
 
 use iced_native::event::{self, Event};
 use iced_native::layout;
@@ -10,8 +11,6 @@ use iced_native::{
 };
 use iced_style::button::StyleSheet;
 
-use std::any::Any;
-
 pub use button::State;
 
 pub struct Button<'a, Message, Renderer> {
@@ -77,20 +76,20 @@ where
     Message: 'static + Clone,
     Renderer: 'static + iced_native::Renderer,
 {
-    fn tag(&self) -> std::any::TypeId {
-        std::any::TypeId::of::<State>()
+    fn tag(&self) -> tree::Tag {
+        tree::Tag::of::<State>()
     }
 
-    fn state(&self) -> Box<dyn Any> {
-        Box::new(State::new())
+    fn state(&self) -> tree::State {
+        tree::State::new(State::new())
     }
 
-    fn diff(&self, tree: &mut Tree) {
-        tree.diff_children(std::slice::from_ref(&self.content))
+    fn children(&self) -> Vec<Tree> {
+        vec![Tree::new(&self.content)]
     }
 
-    fn children_state(&self) -> Vec<Tree> {
-        vec![Tree::new(&self.content)]
+    fn diff(&self, tree: &mut Tree) {
+        tree.diff_children(std::slice::from_ref(&self.content))
     }
 
     fn width(&self) -> Length {
diff --git a/pure/src/widget/checkbox.rs b/pure/src/widget/checkbox.rs
index 5352fad3..8aa4e845 100644
--- a/pure/src/widget/checkbox.rs
+++ b/pure/src/widget/checkbox.rs
@@ -7,8 +7,6 @@ use iced_native::renderer;
 use iced_native::text;
 use iced_native::{Clipboard, Hasher, Length, Point, Rectangle, Shell};
 
-use std::any::{self, Any};
-
 pub use iced_native::widget::Checkbox;
 
 impl<'a, Message, Renderer> Widget<Message, Renderer>
@@ -16,20 +14,6 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
 where
     Renderer: text::Renderer,
 {
-    fn tag(&self) -> any::TypeId {
-        any::TypeId::of::<()>()
-    }
-
-    fn state(&self) -> Box<dyn Any> {
-        Box::new(())
-    }
-
-    fn diff(&self, _tree: &mut Tree) {}
-
-    fn children_state(&self) -> Vec<Tree> {
-        Vec::new()
-    }
-
     fn width(&self) -> Length {
         <Self as iced_native::Widget<Message, Renderer>>::width(self)
     }
diff --git a/pure/src/widget/column.rs b/pure/src/widget/column.rs
index a9d7246e..4ab3e00d 100644
--- a/pure/src/widget/column.rs
+++ b/pure/src/widget/column.rs
@@ -9,7 +9,6 @@ use iced_native::{
     Alignment, Clipboard, Hasher, Length, Padding, Point, Rectangle, Shell,
 };
 
-use std::any::{self, Any};
 use std::u32;
 
 pub struct Column<'a, Message, Renderer> {
@@ -86,22 +85,14 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
 where
     Renderer: iced_native::Renderer,
 {
-    fn tag(&self) -> any::TypeId {
-        any::TypeId::of::<()>()
-    }
-
-    fn state(&self) -> Box<dyn Any> {
-        Box::new(())
+    fn children(&self) -> Vec<Tree> {
+        self.children.iter().map(Tree::new).collect()
     }
 
     fn diff(&self, tree: &mut Tree) {
         tree.diff_children(&self.children);
     }
 
-    fn children_state(&self) -> Vec<Tree> {
-        self.children.iter().map(Tree::new).collect()
-    }
-
     fn width(&self) -> Length {
         self.width
     }
diff --git a/pure/src/widget/container.rs b/pure/src/widget/container.rs
index 85ea8039..f42b127d 100644
--- a/pure/src/widget/container.rs
+++ b/pure/src/widget/container.rs
@@ -11,7 +11,6 @@ use iced_native::{
     Clipboard, Hasher, Layout, Length, Padding, Point, Rectangle, Shell,
 };
 
-use std::any::{self, Any};
 use std::hash::Hash;
 use std::u32;
 
@@ -124,22 +123,14 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
 where
     Renderer: iced_native::Renderer,
 {
-    fn tag(&self) -> any::TypeId {
-        any::TypeId::of::<()>()
-    }
-
-    fn state(&self) -> Box<dyn Any> {
-        Box::new(())
+    fn children(&self) -> Vec<Tree> {
+        vec![Tree::new(&self.content)]
     }
 
     fn diff(&self, tree: &mut Tree) {
         tree.diff_children(std::slice::from_ref(&self.content))
     }
 
-    fn children_state(&self) -> Vec<Tree> {
-        vec![Tree::new(&self.content)]
-    }
-
     fn width(&self) -> Length {
         self.width
     }
diff --git a/pure/src/widget/element.rs b/pure/src/widget/element.rs
index 2a137d40..d905b924 100644
--- a/pure/src/widget/element.rs
+++ b/pure/src/widget/element.rs
@@ -1,4 +1,5 @@
-use crate::widget::{Tree, Widget};
+use crate::widget::tree::{self, Tree};
+use crate::widget::Widget;
 
 use iced_native::event::{self, Event};
 use iced_native::layout::{self, Layout};
@@ -6,8 +7,6 @@ use iced_native::mouse;
 use iced_native::renderer;
 use iced_native::{Clipboard, Hasher, Length, Point, Rectangle, Shell};
 
-use std::any::{self, Any};
-
 pub struct Element<'a, Message, Renderer> {
     widget: Box<dyn Widget<Message, Renderer> + 'a>,
 }
@@ -66,20 +65,20 @@ where
     A: 'a,
     B: 'a,
 {
-    fn tag(&self) -> any::TypeId {
+    fn tag(&self) -> tree::Tag {
         self.widget.tag()
     }
 
-    fn state(&self) -> Box<dyn Any> {
+    fn state(&self) -> tree::State {
         self.widget.state()
     }
 
-    fn diff(&self, tree: &mut Tree) {
-        self.widget.diff(tree)
+    fn children(&self) -> Vec<Tree> {
+        self.widget.children()
     }
 
-    fn children_state(&self) -> Vec<Tree> {
-        self.widget.children_state()
+    fn diff(&self, tree: &mut Tree) {
+        self.widget.diff(tree)
     }
 
     fn width(&self) -> Length {
diff --git a/pure/src/widget/image.rs b/pure/src/widget/image.rs
index 51a24ed1..ce807813 100644
--- a/pure/src/widget/image.rs
+++ b/pure/src/widget/image.rs
@@ -6,7 +6,6 @@ use iced_native::renderer;
 use iced_native::widget::image;
 use iced_native::{Hasher, Length, Point, Rectangle};
 
-use std::any::{self, Any};
 use std::hash::Hash;
 
 pub use image::Image;
@@ -16,20 +15,6 @@ where
     Handle: Clone + Hash,
     Renderer: iced_native::image::Renderer<Handle = Handle>,
 {
-    fn tag(&self) -> any::TypeId {
-        any::TypeId::of::<()>()
-    }
-
-    fn state(&self) -> Box<dyn Any> {
-        Box::new(())
-    }
-
-    fn children_state(&self) -> Vec<Tree> {
-        Vec::new()
-    }
-
-    fn diff(&self, _tree: &mut Tree) {}
-
     fn width(&self) -> Length {
         <Self as iced_native::Widget<Message, Renderer>>::width(self)
     }
diff --git a/pure/src/widget/radio.rs b/pure/src/widget/radio.rs
index 25fe5bdd..233297b3 100644
--- a/pure/src/widget/radio.rs
+++ b/pure/src/widget/radio.rs
@@ -7,8 +7,6 @@ use iced_native::renderer;
 use iced_native::text;
 use iced_native::{Clipboard, Hasher, Length, Point, Rectangle, Shell};
 
-use std::any::{self, Any};
-
 pub use iced_native::widget::Radio;
 
 impl<'a, Message, Renderer> Widget<Message, Renderer>
@@ -17,20 +15,6 @@ where
     Message: Clone,
     Renderer: text::Renderer,
 {
-    fn tag(&self) -> any::TypeId {
-        any::TypeId::of::<()>()
-    }
-
-    fn state(&self) -> Box<dyn Any> {
-        Box::new(())
-    }
-
-    fn diff(&self, _tree: &mut Tree) {}
-
-    fn children_state(&self) -> Vec<Tree> {
-        Vec::new()
-    }
-
     fn width(&self) -> Length {
         <Self as iced_native::Widget<Message, Renderer>>::width(self)
     }
diff --git a/pure/src/widget/row.rs b/pure/src/widget/row.rs
index ec7e144c..1f281446 100644
--- a/pure/src/widget/row.rs
+++ b/pure/src/widget/row.rs
@@ -9,8 +9,6 @@ use iced_native::{
     Alignment, Clipboard, Hasher, Length, Padding, Point, Rectangle, Shell,
 };
 
-use std::any::{self, Any};
-
 pub struct Row<'a, Message, Renderer> {
     spacing: u16,
     padding: Padding,
@@ -77,22 +75,14 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
 where
     Renderer: iced_native::Renderer,
 {
-    fn tag(&self) -> any::TypeId {
-        any::TypeId::of::<()>()
-    }
-
-    fn state(&self) -> Box<dyn Any> {
-        Box::new(())
+    fn children(&self) -> Vec<Tree> {
+        self.children.iter().map(Tree::new).collect()
     }
 
     fn diff(&self, tree: &mut Tree) {
         tree.diff_children(&self.children)
     }
 
-    fn children_state(&self) -> Vec<Tree> {
-        self.children.iter().map(Tree::new).collect()
-    }
-
     fn width(&self) -> Length {
         self.width
     }
diff --git a/pure/src/widget/scrollable.rs b/pure/src/widget/scrollable.rs
index badc9fc2..c3289f9e 100644
--- a/pure/src/widget/scrollable.rs
+++ b/pure/src/widget/scrollable.rs
@@ -1,4 +1,4 @@
-use crate::widget::Tree;
+use crate::widget::tree::{self, Tree};
 use crate::{Element, Widget};
 
 use iced_native::event::{self, Event};
@@ -10,8 +10,6 @@ use iced_native::{Clipboard, Hasher, Length, Point, Rectangle, Shell};
 
 pub use iced_style::scrollable::StyleSheet;
 
-use std::any::{self, Any};
-
 /// A widget that can vertically display an infinite amount of content with a
 /// scrollbar.
 #[allow(missing_debug_implementations)]
@@ -92,20 +90,20 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
 where
     Renderer: iced_native::Renderer,
 {
-    fn tag(&self) -> any::TypeId {
-        any::TypeId::of::<scrollable::State>()
+    fn tag(&self) -> tree::Tag {
+        tree::Tag::of::<scrollable::State>()
     }
 
-    fn state(&self) -> Box<dyn Any> {
-        Box::new(scrollable::State::new())
+    fn state(&self) -> tree::State {
+        tree::State::new(scrollable::State::new())
     }
 
-    fn diff(&self, tree: &mut Tree) {
-        tree.diff_children(std::slice::from_ref(&self.content))
+    fn children(&self) -> Vec<Tree> {
+        vec![Tree::new(&self.content)]
     }
 
-    fn children_state(&self) -> Vec<Tree> {
-        vec![Tree::new(&self.content)]
+    fn diff(&self, tree: &mut Tree) {
+        tree.diff_children(std::slice::from_ref(&self.content))
     }
 
     fn width(&self) -> Length {
diff --git a/pure/src/widget/slider.rs b/pure/src/widget/slider.rs
index f659c2ed..691d3f18 100644
--- a/pure/src/widget/slider.rs
+++ b/pure/src/widget/slider.rs
@@ -1,7 +1,8 @@
 //! Display an interactive selector of a single value from a range of values.
 //!
 //! A [`Slider`] has some local [`State`].
-use crate::{Element, Tree, Widget};
+use crate::widget::tree::{self, Tree};
+use crate::{Element, Widget};
 
 use iced_native::event::{self, Event};
 use iced_native::layout;
@@ -12,7 +13,6 @@ use iced_native::{
     Clipboard, Hasher, Layout, Length, Point, Rectangle, Shell, Size,
 };
 
-use std::any::{self, Any};
 use std::ops::RangeInclusive;
 
 pub use iced_style::slider::{Handle, HandleShape, Style, StyleSheet};
@@ -143,16 +143,12 @@ where
     Message: Clone,
     Renderer: iced_native::Renderer,
 {
-    fn tag(&self) -> any::TypeId {
-        any::TypeId::of::<slider::State>()
+    fn tag(&self) -> tree::Tag {
+        tree::Tag::of::<slider::State>()
     }
 
-    fn state(&self) -> Box<dyn Any> {
-        Box::new(slider::State::new())
-    }
-
-    fn children_state(&self) -> Vec<Tree> {
-        Vec::new()
+    fn state(&self) -> tree::State {
+        tree::State::new(slider::State::new())
     }
 
     fn width(&self) -> Length {
diff --git a/pure/src/widget/space.rs b/pure/src/widget/space.rs
index 67d17c16..d7394398 100644
--- a/pure/src/widget/space.rs
+++ b/pure/src/widget/space.rs
@@ -7,8 +7,6 @@ use iced_native::renderer;
 use iced_native::text;
 use iced_native::{Clipboard, Hasher, Length, Point, Rectangle, Shell};
 
-use std::any::{self, Any};
-
 pub use iced_native::widget::Space;
 
 impl<'a, Message, Renderer> Widget<Message, Renderer> for Space
@@ -16,20 +14,6 @@ where
     Message: Clone,
     Renderer: text::Renderer,
 {
-    fn tag(&self) -> any::TypeId {
-        any::TypeId::of::<()>()
-    }
-
-    fn state(&self) -> Box<dyn Any> {
-        Box::new(())
-    }
-
-    fn diff(&self, _tree: &mut Tree) {}
-
-    fn children_state(&self) -> Vec<Tree> {
-        Vec::new()
-    }
-
     fn width(&self) -> Length {
         <Self as iced_native::Widget<Message, Renderer>>::width(self)
     }
diff --git a/pure/src/widget/text.rs b/pure/src/widget/text.rs
index 8f157ea0..696d0ae1 100644
--- a/pure/src/widget/text.rs
+++ b/pure/src/widget/text.rs
@@ -5,28 +5,12 @@ use iced_native::renderer;
 use iced_native::text;
 use iced_native::{Hasher, Length, Point, Rectangle};
 
-use std::any::{self, Any};
-
 pub use iced_native::widget::Text;
 
 impl<Message, Renderer> Widget<Message, Renderer> for Text<Renderer>
 where
     Renderer: text::Renderer,
 {
-    fn tag(&self) -> any::TypeId {
-        any::TypeId::of::<()>()
-    }
-
-    fn state(&self) -> Box<dyn Any> {
-        Box::new(())
-    }
-
-    fn diff(&self, _tree: &mut Tree) {}
-
-    fn children_state(&self) -> Vec<Tree> {
-        Vec::new()
-    }
-
     fn width(&self) -> Length {
         <Self as iced_native::Widget<Message, Renderer>>::width(self)
     }
diff --git a/pure/src/widget/text_input.rs b/pure/src/widget/text_input.rs
index e18a2bf0..40ce140c 100644
--- a/pure/src/widget/text_input.rs
+++ b/pure/src/widget/text_input.rs
@@ -1,4 +1,5 @@
-use crate::widget::{Element, Tree, Widget};
+use crate::widget::tree::{self, Tree};
+use crate::widget::{Element, Widget};
 
 use iced_native::event::{self, Event};
 use iced_native::layout::{self, Layout};
@@ -12,8 +13,6 @@ use iced_native::{
 
 pub use iced_style::text_input::StyleSheet;
 
-use std::any::{self, Any};
-
 /// A field that can be filled with text.
 ///
 /// # Example
@@ -138,18 +137,12 @@ where
     Message: Clone,
     Renderer: iced_native::text::Renderer,
 {
-    fn tag(&self) -> any::TypeId {
-        any::TypeId::of::<text_input::State>()
-    }
-
-    fn state(&self) -> Box<dyn Any> {
-        Box::new(text_input::State::new())
+    fn tag(&self) -> tree::Tag {
+        tree::Tag::of::<text_input::State>()
     }
 
-    fn diff(&self, _tree: &mut Tree) {}
-
-    fn children_state(&self) -> Vec<Tree> {
-        Vec::new()
+    fn state(&self) -> tree::State {
+        tree::State::new(text_input::State::new())
     }
 
     fn width(&self) -> Length {
diff --git a/pure/src/widget/toggler.rs b/pure/src/widget/toggler.rs
index ec86fff0..08619866 100644
--- a/pure/src/widget/toggler.rs
+++ b/pure/src/widget/toggler.rs
@@ -8,8 +8,6 @@ use iced_native::renderer;
 use iced_native::text;
 use iced_native::{Clipboard, Hasher, Length, Point, Rectangle, Shell};
 
-use std::any::{self, Any};
-
 pub use iced_native::widget::toggler::{Style, StyleSheet, Toggler};
 
 impl<'a, Message, Renderer> Widget<Message, Renderer>
@@ -17,18 +15,6 @@ impl<'a, Message, Renderer> Widget<Message, Renderer>
 where
     Renderer: text::Renderer,
 {
-    fn tag(&self) -> any::TypeId {
-        any::TypeId::of::<()>()
-    }
-
-    fn state(&self) -> Box<dyn Any> {
-        Box::new(())
-    }
-
-    fn children_state(&self) -> Vec<Tree> {
-        Vec::new()
-    }
-
     fn width(&self) -> Length {
         <Self as iced_native::Widget<Message, Renderer>>::width(self)
     }
diff --git a/pure/src/widget/tree.rs b/pure/src/widget/tree.rs
index 3a5f4433..33f5693a 100644
--- a/pure/src/widget/tree.rs
+++ b/pure/src/widget/tree.rs
@@ -3,7 +3,7 @@ use crate::widget::Element;
 use std::any::{self, Any};
 
 pub struct Tree {
-    pub tag: any::TypeId,
+    pub tag: Tag,
     pub state: State,
     pub children: Vec<Tree>,
 }
@@ -11,8 +11,8 @@ pub struct Tree {
 impl Tree {
     pub fn empty() -> Self {
         Self {
-            tag: any::TypeId::of::<()>(),
-            state: State(Box::new(())),
+            tag: Tag::stateless(),
+            state: State::None,
             children: Vec::new(),
         }
     }
@@ -22,8 +22,8 @@ impl Tree {
     ) -> Self {
         Self {
             tag: element.as_widget().tag(),
-            state: State(element.as_widget().state()),
-            children: element.as_widget().children_state(),
+            state: element.as_widget().state(),
+            children: element.as_widget().children(),
         }
     }
 
@@ -60,20 +60,56 @@ impl Tree {
     }
 }
 
-pub struct State(Box<dyn Any>);
+#[derive(Debug, Clone, Copy, PartialOrd, Ord, PartialEq, Eq, Hash)]
+pub struct Tag(any::TypeId);
+
+impl Tag {
+    pub fn of<T>() -> Self
+    where
+        T: 'static,
+    {
+        Self(any::TypeId::of::<T>())
+    }
+
+    pub fn stateless() -> Self {
+        Self::of::<()>()
+    }
+}
+
+pub enum State {
+    None,
+    Some(Box<dyn Any>),
+}
 
 impl State {
+    pub fn new<T>(state: T) -> Self
+    where
+        T: 'static,
+    {
+        State::Some(Box::new(state))
+    }
+
     pub fn downcast_ref<T>(&self) -> &T
     where
         T: 'static,
     {
-        self.0.downcast_ref().expect("Downcast widget state")
+        match self {
+            State::None => panic!("Downcast on stateless state"),
+            State::Some(state) => {
+                state.downcast_ref().expect("Downcast widget state")
+            }
+        }
     }
 
     pub fn downcast_mut<T>(&mut self) -> &mut T
     where
         T: 'static,
     {
-        self.0.downcast_mut().expect("Downcast widget state")
+        match self {
+            State::None => panic!("Downcast on stateless state"),
+            State::Some(state) => {
+                state.downcast_mut().expect("Downcast widget state")
+            }
+        }
     }
 }