add class and style interfaces

Cargo.toml

@@ -6,7 +6,7 @@ members = [
     "crates/xilem_web/web_examples/counter_custom_element",
     "crates/xilem_web/web_examples/todomvc",
     "crates/xilem_web/web_examples/mathml_svg",
-    "crates/xilem_web/web_examples/svgtoy",
+    "crates/xilem_web/web_examples/svgtoy", 
 ]
 
 [workspace.package]

crates/xilem_web/Cargo.toml

@@ -34,7 +34,9 @@ peniko = { git = "https://github.com/linebender/peniko", rev = "629fc3325b016a8c
 version = "0.3.4"
 features = [
     "console",
+    "CssStyleDeclaration",
     "Document",
+    "DomTokenList",
     "Element",
     "Event",
     "HtmlElement",

crates/xilem_web/src/class.rs

@@ -0,0 +1,118 @@
+use std::{borrow::Cow, marker::PhantomData};
+
+use xilem_core::{Id, MessageResult};
+
+use crate::{
+    interfaces::{sealed::Sealed, Element},
+    ChangeFlags, Cx, View, ViewMarker,
+};
+
+/// A trait to make the class adding functions generic over collection type
+pub trait IntoClasses {
+    fn into_classes(self, classes: &mut Vec<Cow<'static, str>>);
+}
+
+impl IntoClasses for String {
+    fn into_classes(self, classes: &mut Vec<Cow<'static, str>>) {
+        classes.push(self.into());
+    }
+}
+
+impl IntoClasses for &'static str {
+    fn into_classes(self, classes: &mut Vec<Cow<'static, str>>) {
+        classes.push(self.into())
+    }
+}
+
+impl<T> IntoClasses for Option<T>
+where
+    T: IntoClasses,
+{
+    fn into_classes(self, classes: &mut Vec<Cow<'static, str>>) {
+        if let Some(t) = self {
+            t.into_classes(classes)
+        }
+    }
+}
+
+impl<T> IntoClasses for Vec<T>
+where
+    T: IntoClasses,
+{
+    fn into_classes(self, classes: &mut Vec<Cow<'static, str>>) {
+        for itm in self {
+            itm.into_classes(classes);
+        }
+    }
+}
+
+macro_rules! impl_tuple_intoclasses {
+    ($($name:ident : $type:ident),* $(,)?) => {
+        impl<$($type),*> IntoClasses for ($($type,)*)
+        where
+            $($type: IntoClasses),*
+        {
+            #[allow(unused_variables)]
+            fn into_classes(self, classes: &mut Vec<Cow<'static, str>>) {
+                let ($($name,)*) = self;
+                $(
+                    $name.into_classes(classes);
+                )*
+            }
+        }
+    };
+}
+
+impl_tuple_intoclasses!();
+impl_tuple_intoclasses!(t1: T1);
+impl_tuple_intoclasses!(t1: T1, t2: T2);
+impl_tuple_intoclasses!(t1: T1, t2: T2, t3: T3);
+impl_tuple_intoclasses!(t1: T1, t2: T2, t3: T3, t4: T4);
+
+/// Applies a class to the underlying element.
+pub struct Class<E, T, A> {
+    pub(crate) element: E,
+    pub(crate) class_names: Vec<Cow<'static, str>>,
+    pub(crate) phantom: PhantomData<fn() -> (T, A)>,
+}
+
+impl<E, T, A> ViewMarker for Class<E, T, A> {}
+impl<E, T, A> Sealed for Class<E, T, A> {}
+
+impl<E: Element<T, A>, T, A> View<T, A> for Class<E, T, A> {
+    type State = E::State;
+    type Element = E::Element;
+
+    fn build(&self, cx: &mut Cx) -> (Id, Self::State, Self::Element) {
+        for class_name in &self.class_names {
+            cx.add_class_to_element(class_name);
+        }
+        self.element.build(cx)
+    }
+
+    fn rebuild(
+        &self,
+        cx: &mut Cx,
+        prev: &Self,
+        id: &mut Id,
+        state: &mut Self::State,
+        element: &mut Self::Element,
+    ) -> ChangeFlags {
+        for class_name in &self.class_names {
+            cx.add_class_to_element(class_name);
+        }
+        self.element.rebuild(cx, &prev.element, id, state, element)
+    }
+
+    fn message(
+        &self,
+        id_path: &[Id],
+        state: &mut Self::State,
+        message: Box<dyn std::any::Any>,
+        app_state: &mut T,
+    ) -> MessageResult<A> {
+        self.element.message(id_path, state, message, app_state)
+    }
+}
+
+crate::interfaces::impl_dom_interfaces_for_ty!(Element, Class);