Draft widget operations

native/src/widget/action.rs

@@ -0,0 +1,78 @@
+use crate::widget::state;
+use crate::widget::{Id, Operation};
+
+use iced_futures::MaybeSend;
+
+pub struct Action<T>(Box<dyn Operation<T>>);
+
+impl<T> Action<T> {
+    pub fn new(operation: impl Operation<T> + 'static) -> Self {
+        Self(Box::new(operation))
+    }
+
+    pub fn map<A>(
+        self,
+        f: impl Fn(T) -> A + 'static + MaybeSend + Sync,
+    ) -> Action<A>
+    where
+        T: 'static,
+        A: 'static,
+    {
+        Action(Box::new(Map {
+            operation: self.0,
+            f: Box::new(f),
+        }))
+    }
+
+    pub fn into_operation(self) -> Box<dyn Operation<T>> {
+        self.0
+    }
+}
+
+struct Map<A, B> {
+    operation: Box<dyn Operation<A>>,
+    f: Box<dyn Fn(A) -> B>,
+}
+
+impl<A, B> Operation<B> for Map<A, B>
+where
+    A: 'static,
+    B: 'static,
+{
+    fn container(
+        &mut self,
+        id: Option<&Id>,
+        operate_on_children: &dyn Fn(&mut dyn Operation<B>),
+    ) {
+        struct MapRef<'a, A, B> {
+            operation: &'a mut dyn Operation<A>,
+            f: &'a dyn Fn(A) -> B,
+        }
+
+        impl<'a, A, B> Operation<B> for MapRef<'a, A, B> {
+            fn container(
+                &mut self,
+                id: Option<&Id>,
+                operate_on_children: &dyn Fn(&mut dyn Operation<B>),
+            ) {
+                let Self { operation, f } = self;
+
+                operation.container(id, &|operation| {
+                    operate_on_children(&mut MapRef { operation, f });
+                });
+            }
+        }
+
+        let Self { operation, f } = self;
+
+        MapRef {
+            operation: operation.as_mut(),
+            f,
+        }
+        .container(id, operate_on_children);
+    }
+
+    fn focusable(&mut self, state: &mut dyn state::Focusable, id: Option<&Id>) {
+        self.operation.focusable(state, id);
+    }
+}