Fine-tune `Catalog` approach for `button`, `checkbox`, and `svg`

9 files changed, 167 insertions, 149 deletions

diff --git a/Cargo.toml b/Cargo.toml
index b82c0f67..fdd503c9 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -50,7 +50,7 @@ highlighter = ["iced_highlighter"]
 # Enables experimental multi-window support.
 multi-window = ["iced_winit/multi-window"]
 # Enables the advanced module
-advanced = []
+advanced = ["iced_widget/advanced"]
 # Enables embedding Fira Sans as the default font on Wasm builds
 fira-sans = ["iced_renderer/fira-sans"]
 # Enables auto-detecting light/dark mode for the built-in theme
diff --git a/core/src/closure.rs b/core/src/closure.rs
deleted file mode 100644
index dc7b4fee..00000000
--- a/core/src/closure.rs
+++ /dev/null
@@ -1,33 +0,0 @@
-//! Box closures with ease.
-//!
-//! These are just a bunch of types that wrap boxed closures with
-//! blanket [`From`] implementations for easy conversions.
-//!
-//! Mainly, it allows functions to take `Into<T>` where `T` may end
-//! up being a boxed closure.
-
-/// A boxed closure that takes `A` by reference and produces `O`.
-#[allow(missing_debug_implementations)]
-pub struct Unary<'a, A, O>(pub Box<dyn Fn(&A) -> O + 'a>);
-
-impl<'a, A, O, T> From<T> for Unary<'a, A, O>
-where
-    T: Fn(&A) -> O + 'a,
-{
-    fn from(f: T) -> Self {
-        Self(Box::new(f))
-    }
-}
-
-/// A boxed closure that takes `A` by reference and `B` by value and produces `O`.
-#[allow(missing_debug_implementations)]
-pub struct Binary<'a, A, B, O>(pub Box<dyn Fn(&A, B) -> O + 'a>);
-
-impl<'a, A, B, O, T> From<T> for Binary<'a, A, B, O>
-where
-    T: Fn(&A, B) -> O + 'a,
-{
-    fn from(f: T) -> Self {
-        Self(Box::new(f))
-    }
-}
diff --git a/core/src/lib.rs b/core/src/lib.rs
index 36b47d80..d076413e 100644
--- a/core/src/lib.rs
+++ b/core/src/lib.rs
@@ -19,7 +19,6 @@
 pub mod alignment;
 pub mod border;
 pub mod clipboard;
-pub mod closure;
 pub mod event;
 pub mod font;
 pub mod gradient;
diff --git a/examples/svg/src/main.rs b/examples/svg/src/main.rs
index cc686dca..0dcf9bc1 100644
--- a/examples/svg/src/main.rs
+++ b/examples/svg/src/main.rs
@@ -31,7 +31,7 @@ impl Tiger {
         ));
 
         let svg = svg(handle).width(Length::Fill).height(Length::Fill).style(
-            |_theme, _status| svg::Appearance {
+            |_theme, _status| svg::Style {
                 color: if self.apply_color_filter {
                     Some(color!(0x0000ff))
                 } else {
diff --git a/widget/Cargo.toml b/widget/Cargo.toml
index 3c9ffddb..a45f47ef 100644
--- a/widget/Cargo.toml
+++ b/widget/Cargo.toml
@@ -21,6 +21,7 @@ svg = ["iced_renderer/svg"]
 canvas = ["iced_renderer/geometry"]
 qr_code = ["canvas", "qrcode"]
 wgpu = ["iced_renderer/wgpu"]
+advanced = []
 
 [dependencies]
 iced_renderer.workspace = true
diff --git a/widget/src/button.rs b/widget/src/button.rs
index 8754622f..80a18e82 100644
--- a/widget/src/button.rs
+++ b/widget/src/button.rs
@@ -1,5 +1,4 @@
 //! Allow your users to perform actions by pressing a button.
-use crate::core::closure;
 use crate::core::event::{self, Event};
 use crate::core::layout;
 use crate::core::mouse;
@@ -58,7 +57,7 @@ where
     height: Length,
     padding: Padding,
     clip: bool,
-    style: Theme::Item<'a>,
+    class: Theme::Class<'a>,
 }
 
 impl<'a, Message, Theme, Renderer> Button<'a, Message, Theme, Renderer>
@@ -80,7 +79,7 @@ where
             height: size.height.fluid(),
             padding: DEFAULT_PADDING,
             clip: false,
-            style: Theme::default(),
+            class: Theme::default(),
         }
     }
 
@@ -119,18 +118,30 @@ where
         self
     }
 
-    /// Sets the style variant of this [`Button`].
-    pub fn style(mut self, style: impl Into<Theme::Item<'a>>) -> Self {
-        self.style = style.into();
-        self
-    }
-
     /// Sets whether the contents of the [`Button`] should be clipped on
     /// overflow.
     pub fn clip(mut self, clip: bool) -> Self {
         self.clip = clip;
         self
     }
+
+    /// Sets the style of this [`Button`].
+    #[must_use]
+    pub fn style(mut self, style: impl Fn(&Theme, Status) -> Style + 'a) -> Self
+    where
+        Theme::Class<'a>: From<StyleFn<'a, Theme>>,
+    {
+        self.class = (Box::new(style) as StyleFn<'a, Theme>).into();
+        self
+    }
+
+    /// Sets the style class of this [`Button`].
+    #[cfg(feature = "advanced")]
+    #[must_use]
+    pub fn class(mut self, class: impl Into<Theme::Class<'a>>) -> Self {
+        self.class = class.into();
+        self
+    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
@@ -302,19 +313,19 @@ where
             Status::Active
         };
 
-        let styling = theme.style(&self.style, status);
+        let style = theme.style(&self.class, status);
 
-        if styling.background.is_some()
-            || styling.border.width > 0.0
-            || styling.shadow.color.a > 0.0
+        if style.background.is_some()
+            || style.border.width > 0.0
+            || style.shadow.color.a > 0.0
         {
             renderer.fill_quad(
                 renderer::Quad {
                     bounds,
-                    border: styling.border,
-                    shadow: styling.shadow,
+                    border: style.border,
+                    shadow: style.shadow,
                 },
-                styling
+                style
                     .background
                     .unwrap_or(Background::Color(Color::TRANSPARENT)),
             );
@@ -331,7 +342,7 @@ where
             renderer,
             theme,
             &renderer::Style {
-                text_color: styling.text_color,
+                text_color: style.text_color,
             },
             content_layout,
             cursor,
@@ -405,7 +416,7 @@ pub enum Status {
     Disabled,
 }
 
-/// The appearance of a button.
+/// The style of a button.
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub struct Style {
     /// The [`Background`] of the button.
@@ -419,7 +430,7 @@ pub struct Style {
 }
 
 impl Style {
-    /// Updates the [`Appearance`] with the given [`Background`].
+    /// Updates the [`Style`] with the given [`Background`].
     pub fn with_background(self, background: impl Into<Background>) -> Self {
         Self {
             background: Some(background.into()),
@@ -428,7 +439,7 @@ impl Style {
     }
 }
 
-impl std::default::Default for Style {
+impl Default for Style {
     fn default() -> Self {
         Self {
             background: None,
@@ -441,30 +452,30 @@ impl std::default::Default for Style {
 
 /// The theme catalog of a [`Button`].
 pub trait Catalog: Sized {
-    /// The item type of this [`Catalog`].
-    type Item<'a>;
+    /// The item class of this [`Catalog`].
+    type Class<'a>;
 
-    /// The default item produced by this [`Catalog`].
-    fn default<'a>() -> Self::Item<'a>;
+    /// The default class produced by this [`Catalog`].
+    fn default<'a>() -> Self::Class<'a>;
 
-    /// The [`Style`] of an item with the given status.
-    fn style(&self, item: &Self::Item<'_>, status: Status) -> Style;
+    /// The [`Style`] of a class with the given status.
+    fn style(&self, item: &Self::Class<'_>, status: Status) -> Style;
 }
 
-/// The item of a button [`Catalog`] for the built-in [`Theme`].
+/// A styling function for a [`Button`].
 ///
 /// This is just a boxed closure: `Fn(&Theme, Status) -> Style`.
-pub type Item<'a, Theme> = closure::Binary<'a, Theme, Status, Style>;
+pub type StyleFn<'a, Theme> = Box<dyn Fn(&Theme, Status) -> Style + 'a>;
 
 impl Catalog for Theme {
-    type Item<'a> = Item<'a, Self>;
+    type Class<'a> = StyleFn<'a, Self>;
 
-    fn default<'a>() -> Self::Item<'a> {
-        closure::Binary::from(primary)
+    fn default<'a>() -> Self::Class<'a> {
+        Box::new(primary)
     }
 
-    fn style(&self, item: &Self::Item<'_>, status: Status) -> Style {
-        (item.0)(self, status)
+    fn style(&self, class: &Self::Class<'_>, status: Status) -> Style {
+        class(self, status)
     }
 }
 
@@ -556,12 +567,12 @@ fn styled(pair: palette::Pair) -> Style {
     }
 }
 
-fn disabled(appearance: Style) -> Style {
+fn disabled(style: Style) -> Style {
     Style {
-        background: appearance
+        background: style
             .background
             .map(|background| background.scale_alpha(0.5)),
-        text_color: appearance.text_color.scale_alpha(0.5),
-        ..appearance
+        text_color: style.text_color.scale_alpha(0.5),
+        ..style
     }
 }
diff --git a/widget/src/checkbox.rs b/widget/src/checkbox.rs
index 15fb8f58..a90914b8 100644
--- a/widget/src/checkbox.rs
+++ b/widget/src/checkbox.rs
@@ -39,6 +39,7 @@ pub struct Checkbox<
     Renderer = crate::Renderer,
 > where
     Renderer: text::Renderer,
+    Theme: Catalog,
 {
     is_checked: bool,
     on_toggle: Option<Box<dyn Fn(bool) -> Message + 'a>>,
@@ -51,12 +52,13 @@ pub struct Checkbox<
     text_shaping: text::Shaping,
     font: Option<Renderer::Font>,
     icon: Icon<Renderer::Font>,
-    style: Style<'a, Theme>,
+    class: Theme::Class<'a>,
 }
 
 impl<'a, Message, Theme, Renderer> Checkbox<'a, Message, Theme, Renderer>
 where
     Renderer: text::Renderer,
+    Theme: Catalog,
 {
     /// The default size of a [`Checkbox`].
     const DEFAULT_SIZE: f32 = 16.0;
@@ -69,10 +71,7 @@ where
     /// It expects:
     ///   * the label of the [`Checkbox`]
     ///   * a boolean describing whether the [`Checkbox`] is checked or not
-    pub fn new(label: impl Into<String>, is_checked: bool) -> Self
-    where
-        Theme: DefaultStyle + 'a,
-    {
+    pub fn new(label: impl Into<String>, is_checked: bool) -> Self {
         Checkbox {
             is_checked,
             on_toggle: None,
@@ -91,7 +90,7 @@ where
                 line_height: text::LineHeight::default(),
                 shaping: text::Shaping::Basic,
             },
-            style: Box::new(Theme::default_style),
+            class: Theme::default(),
         }
     }
 
@@ -173,12 +172,21 @@ where
         self
     }
 
-    /// Sets the style of the [`Checkbox`].
-    pub fn style(
-        mut self,
-        style: impl Fn(&Theme, Status) -> Appearance + 'a,
-    ) -> Self {
-        self.style = Box::new(style);
+    /// Sets the style of this [`Checkbox`].
+    #[must_use]
+    pub fn style(mut self, style: impl Fn(&Theme, Status) -> Style + 'a) -> Self
+    where
+        Theme::Class<'a>: From<StyleFn<'a, Theme>>,
+    {
+        self.class = (Box::new(style) as StyleFn<'a, Theme>).into();
+        self
+    }
+
+    /// Sets the style class of this [`Checkbox`].
+    #[cfg(feature = "advanced")]
+    #[must_use]
+    pub fn class(mut self, class: impl Into<Theme::Class<'a>>) -> Self {
+        self.class = class.into();
         self
     }
 }
@@ -187,6 +195,7 @@ impl<'a, Message, Theme, Renderer> Widget<Message, Theme, Renderer>
     for Checkbox<'a, Message, Theme, Renderer>
 where
     Renderer: text::Renderer,
+    Theme: Catalog,
 {
     fn tag(&self) -> tree::Tag {
         tree::Tag::of::<widget::text::State<Renderer::Paragraph>>()
@@ -285,7 +294,7 @@ where
         tree: &Tree,
         renderer: &mut Renderer,
         theme: &Theme,
-        style: &renderer::Style,
+        defaults: &renderer::Style,
         layout: Layout<'_>,
         cursor: mouse::Cursor,
         viewport: &Rectangle,
@@ -304,7 +313,7 @@ where
             Status::Active { is_checked }
         };
 
-        let appearance = (self.style)(theme, status);
+        let style = theme.style(&self.class, status);
 
         {
             let layout = children.next().unwrap();
@@ -313,10 +322,10 @@ where
             renderer.fill_quad(
                 renderer::Quad {
                     bounds,
-                    border: appearance.border,
+                    border: style.border,
                     ..renderer::Quad::default()
                 },
-                appearance.background,
+                style.background,
             );
 
             let Icon {
@@ -341,7 +350,7 @@ where
                         shaping: *shaping,
                     },
                     bounds.center(),
-                    appearance.icon_color,
+                    style.icon_color,
                     *viewport,
                 );
             }
@@ -352,11 +361,11 @@ where
 
             crate::text::draw(
                 renderer,
-                style,
+                defaults,
                 label_layout,
                 tree.state.downcast_ref(),
                 crate::text::Appearance {
-                    color: appearance.text_color,
+                    color: style.text_color,
                 },
                 viewport,
             );
@@ -368,7 +377,7 @@ impl<'a, Message, Theme, Renderer> From<Checkbox<'a, Message, Theme, Renderer>>
     for Element<'a, Message, Theme, Renderer>
 where
     Message: 'a,
-    Theme: 'a,
+    Theme: 'a + Catalog,
     Renderer: 'a + text::Renderer,
 {
     fn from(
@@ -413,9 +422,9 @@ pub enum Status {
     },
 }
 
-/// The appearance of a checkbox.
+/// The style of a checkbox.
 #[derive(Debug, Clone, Copy)]
-pub struct Appearance {
+pub struct Style {
     /// The [`Background`] of the checkbox.
     pub background: Background,
     /// The icon [`Color`] of the checkbox.
@@ -426,29 +435,37 @@ pub struct Appearance {
     pub text_color: Option<Color>,
 }
 
-/// The style of a [`Checkbox`].
-pub type Style<'a, Theme> = Box<dyn Fn(&Theme, Status) -> Appearance + 'a>;
+/// The theme catalog of a [`Checkbox`].
+pub trait Catalog: Sized {
+    /// The item class of this [`Catalog`].
+    type Class<'a>;
 
-/// The default style of a [`Checkbox`].
-pub trait DefaultStyle {
-    /// Returns the default style of a [`Checkbox`].
-    fn default_style(&self, status: Status) -> Appearance;
+    /// The default class produced by this [`Catalog`].
+    fn default<'a>() -> Self::Class<'a>;
+
+    /// The [`Style`] of a class with the given status.
+    fn style(&self, item: &Self::Class<'_>, status: Status) -> Style;
 }
 
-impl DefaultStyle for Theme {
-    fn default_style(&self, status: Status) -> Appearance {
-        primary(self, status)
+/// A styling function for a [`Checkbox`].
+///
+/// This is just a boxed closure: `Fn(&Theme, Status) -> Style`.
+pub type StyleFn<'a, Theme> = Box<dyn Fn(&Theme, Status) -> Style + 'a>;
+
+impl Catalog for Theme {
+    type Class<'a> = StyleFn<'a, Self>;
+
+    fn default<'a>() -> Self::Class<'a> {
+        Box::new(primary)
     }
-}
 
-impl DefaultStyle for Appearance {
-    fn default_style(&self, _status: Status) -> Appearance {
-        *self
+    fn style(&self, class: &Self::Class<'_>, status: Status) -> Style {
+        class(self, status)
     }
 }
 
 /// A primary checkbox; denoting a main toggle.
-pub fn primary(theme: &Theme, status: Status) -> Appearance {
+pub fn primary(theme: &Theme, status: Status) -> Style {
     let palette = theme.extended_palette();
 
     match status {
@@ -474,7 +491,7 @@ pub fn primary(theme: &Theme, status: Status) -> Appearance {
 }
 
 /// A secondary checkbox; denoting a complementary toggle.
-pub fn secondary(theme: &Theme, status: Status) -> Appearance {
+pub fn secondary(theme: &Theme, status: Status) -> Style {
     let palette = theme.extended_palette();
 
     match status {
@@ -500,7 +517,7 @@ pub fn secondary(theme: &Theme, status: Status) -> Appearance {
 }
 
 /// A success checkbox; denoting a positive toggle.
-pub fn success(theme: &Theme, status: Status) -> Appearance {
+pub fn success(theme: &Theme, status: Status) -> Style {
     let palette = theme.extended_palette();
 
     match status {
@@ -526,7 +543,7 @@ pub fn success(theme: &Theme, status: Status) -> Appearance {
 }
 
 /// A danger checkbox; denoting a negaive toggle.
-pub fn danger(theme: &Theme, status: Status) -> Appearance {
+pub fn danger(theme: &Theme, status: Status) -> Style {
     let palette = theme.extended_palette();
 
     match status {
@@ -556,8 +573,8 @@ fn styled(
     base: palette::Pair,
     accent: palette::Pair,
     is_checked: bool,
-) -> Appearance {
-    Appearance {
+) -> Style {
+    Style {
         background: Background::Color(if is_checked {
             accent.color
         } else {
diff --git a/widget/src/helpers.rs b/widget/src/helpers.rs
index e60096d1..4c4d1012 100644
--- a/widget/src/helpers.rs
+++ b/widget/src/helpers.rs
@@ -161,7 +161,7 @@ pub fn checkbox<'a, Message, Theme, Renderer>(
     is_checked: bool,
 ) -> Checkbox<'a, Message, Theme, Renderer>
 where
-    Theme: checkbox::DefaultStyle + 'a,
+    Theme: checkbox::Catalog + 'a,
     Renderer: core::text::Renderer,
 {
     Checkbox::new(label, is_checked)
@@ -367,7 +367,7 @@ pub fn svg<'a, Theme>(
     handle: impl Into<core::svg::Handle>,
 ) -> crate::Svg<'a, Theme>
 where
-    Theme: crate::svg::DefaultStyle + 'a,
+    Theme: crate::svg::Catalog,
 {
     crate::Svg::new(handle)
 }
diff --git a/widget/src/svg.rs b/widget/src/svg.rs
index 1ac07ade..d2fd0aee 100644
--- a/widget/src/svg.rs
+++ b/widget/src/svg.rs
@@ -20,36 +20,36 @@ pub use crate::core::svg::Handle;
 /// [`Svg`] images can have a considerable rendering cost when resized,
 /// specially when they are complex.
 #[allow(missing_debug_implementations)]
-pub struct Svg<'a, Theme = crate::Theme> {
+pub struct Svg<'a, Theme = crate::Theme>
+where
+    Theme: Catalog,
+{
     handle: Handle,
     width: Length,
     height: Length,
     content_fit: ContentFit,
-    style: Style<'a, Theme>,
+    class: Theme::Class<'a>,
 }
 
-impl<'a, Theme> Svg<'a, Theme> {
+impl<'a, Theme> Svg<'a, Theme>
+where
+    Theme: Catalog,
+{
     /// Creates a new [`Svg`] from the given [`Handle`].
-    pub fn new(handle: impl Into<Handle>) -> Self
-    where
-        Theme: DefaultStyle + 'a,
-    {
+    pub fn new(handle: impl Into<Handle>) -> Self {
         Svg {
             handle: handle.into(),
             width: Length::Fill,
             height: Length::Shrink,
             content_fit: ContentFit::Contain,
-            style: Box::new(Theme::default_style),
+            class: Theme::default(),
         }
     }
 
     /// Creates a new [`Svg`] that will display the contents of the file at the
     /// provided path.
     #[must_use]
-    pub fn from_path(path: impl Into<PathBuf>) -> Self
-    where
-        Theme: DefaultStyle + 'a,
-    {
+    pub fn from_path(path: impl Into<PathBuf>) -> Self {
         Self::new(Handle::from_path(path))
     }
 
@@ -78,13 +78,21 @@ impl<'a, Theme> Svg<'a, Theme> {
         }
     }
 
-    /// Sets the style variant of this [`Svg`].
+    /// Sets the style of this [`Svg`].
+    #[must_use]
+    pub fn style(mut self, style: impl Fn(&Theme, Status) -> Style + 'a) -> Self
+    where
+        Theme::Class<'a>: From<StyleFn<'a, Theme>>,
+    {
+        self.class = (Box::new(style) as StyleFn<'a, Theme>).into();
+        self
+    }
+
+    /// Sets the style class of this [`Svg`].
+    #[cfg(feature = "advanced")]
     #[must_use]
-    pub fn style(
-        mut self,
-        style: impl Fn(&Theme, Status) -> Appearance + 'a,
-    ) -> Self {
-        self.style = Box::new(style);
+    pub fn class(mut self, class: impl Into<Theme::Class<'a>>) -> Self {
+        self.class = class.into();
         self
     }
 }
@@ -93,6 +101,7 @@ impl<'a, Message, Theme, Renderer> Widget<Message, Theme, Renderer>
     for Svg<'a, Theme>
 where
     Renderer: svg::Renderer,
+    Theme: Catalog,
 {
     fn size(&self) -> Size<Length> {
         Size {
@@ -167,7 +176,7 @@ where
                 Status::Idle
             };
 
-            let appearance = (self.style)(theme, status);
+            let appearance = theme.style(&self.class, status);
 
             renderer.draw(
                 self.handle.clone(),
@@ -189,7 +198,7 @@ where
 impl<'a, Message, Theme, Renderer> From<Svg<'a, Theme>>
     for Element<'a, Message, Theme, Renderer>
 where
-    Theme: 'a,
+    Theme: Catalog + 'a,
     Renderer: svg::Renderer + 'a,
 {
     fn from(icon: Svg<'a, Theme>) -> Element<'a, Message, Theme, Renderer> {
@@ -208,7 +217,7 @@ pub enum Status {
 
 /// The appearance of an [`Svg`].
 #[derive(Debug, Clone, Copy, PartialEq, Default)]
-pub struct Appearance {
+pub struct Style {
     /// The [`Color`] filter of an [`Svg`].
     ///
     /// Useful for coloring a symbolic icon.
@@ -217,23 +226,37 @@ pub struct Appearance {
     pub color: Option<Color>,
 }
 
-/// The style of an [`Svg`].
-pub type Style<'a, Theme> = Box<dyn Fn(&Theme, Status) -> Appearance + 'a>;
+/// The theme catalog of an [`Svg`].
+pub trait Catalog {
+    /// The item class of this [`Catalog`].
+    type Class<'a>;
+
+    /// The default class produced by this [`Catalog`].
+    fn default<'a>() -> Self::Class<'a>;
 
-/// The default style of an [`Svg`].
-pub trait DefaultStyle {
-    /// Returns the default style of an [`Svg`].
-    fn default_style(&self, status: Status) -> Appearance;
+    /// The [`Style`] of a class with the given status.
+    fn style(&self, class: &Self::Class<'_>, status: Status) -> Style;
 }
 
-impl DefaultStyle for Theme {
-    fn default_style(&self, _status: Status) -> Appearance {
-        Appearance::default()
+impl Catalog for Theme {
+    type Class<'a> = StyleFn<'a, Self>;
+
+    fn default<'a>() -> Self::Class<'a> {
+        Box::new(|_theme, _status| Style::default())
+    }
+
+    fn style(&self, class: &Self::Class<'_>, status: Status) -> Style {
+        class(self, status)
     }
 }
 
-impl DefaultStyle for Appearance {
-    fn default_style(&self, _status: Status) -> Appearance {
-        *self
+/// A styling function for an [`Svg`].
+///
+/// This is just a boxed closure: `Fn(&Theme, Status) -> Style`.
+pub type StyleFn<'a, Theme> = Box<dyn Fn(&Theme, Status) -> Style + 'a>;
+
+impl<'a, Theme> From<Style> for StyleFn<'a, Theme> {
+    fn from(style: Style) -> Self {
+        Box::new(move |_theme, _status| style)
     }
 }