Add create_updater and create_stateful_updater (#172)

reactive/src/effect.rs

@@ -38,7 +38,7 @@ where
 /// Create an Effect that runs the given function whenever the Signals that subscribed
 /// to it in the function.
 ///
-/// The given function will be run immdietly once, and tracks all the signals that
+/// The given function will be run immediately once, and tracks all the signals that
 /// subscribed in that run. And when these Signals update, it will rerun the function.
 /// And the effect re-tracks the signals in each run, so that it will only be re-run
 /// by the Signals that actually ran in the last effect run.
@@ -59,6 +59,62 @@ where
     run_effect(effect);
 }
 
+struct UpdaterEffect<T, I, C, U>
+where
+    C: Fn(Option<T>) -> (I, T),
+    U: Fn(I, T) -> T,
+{
+    id: Id,
+    compute: C,
+    on_change: U,
+    value: RefCell<Box<dyn Any>>,
+    ty: PhantomData<T>,
+    observers: RefCell<Option<HashSet<Id>>>,
+}
+
+impl<T, I, C, U> Drop for UpdaterEffect<T, I, C, U>
+where
+    C: Fn(Option<T>) -> (I, T),
+    U: Fn(I, T) -> T,
+{
+    fn drop(&mut self) {
+        self.id.dispose();
+    }
+}
+
+/// Create an effect updater that runs `on_change` when any signals `compute` subscribes to
+/// changes. `compute` is immediately run and its return value is returned from `create_updater`.
+pub fn create_updater<R>(compute: impl Fn() -> R + 'static, on_change: impl Fn(R) + 'static) -> R
+where
+    R: 'static,
+{
+    create_stateful_updater(move |_| (compute(), ()), move |r, _| on_change(r))
+}
+
+/// Create an effect updater that runs `on_change` when any signals `compute` subscribes to
+/// changes. `compute` is immediately run and its return value is returned from `create_updater`.
+pub fn create_stateful_updater<T, R>(
+    compute: impl Fn(Option<T>) -> (R, T) + 'static,
+    on_change: impl Fn(R, T) -> T + 'static,
+) -> R
+where
+    T: Any + 'static,
+    R: 'static,
+{
+    let id = Id::next();
+    let effect = Rc::new(UpdaterEffect {
+        id,
+        compute,
+        on_change,
+        value: RefCell::new(Box::new(None::<T>)),
+        ty: PhantomData,
+        observers: RefCell::new(None),
+    });
+    id.set_scope();
+
+    run_initial_updater_effect(effect)
+}
+
 /// Signals that's wrapped this untrack will not subscribe to any effect
 pub fn untrack<T>(f: impl FnOnce() -> T) -> T {
     let prev_effect = RUNTIME.with(|runtime| runtime.current_effect.borrow_mut().take());
@@ -111,6 +167,39 @@ pub(crate) fn run_effect(effect: Rc<dyn EffectTrait>) {
     });
 }
 
+fn run_initial_updater_effect<T, I, C, U>(effect: Rc<UpdaterEffect<T, I, C, U>>) -> I
+where
+    T: 'static,
+    I: 'static,
+    C: Fn(Option<T>) -> (I, T) + 'static,
+    U: Fn(I, T) -> T + 'static,
+{
+    let effect_id = effect.id();
+
+    let result = RUNTIME.with(|runtime| {
+        *runtime.current_effect.borrow_mut() = Some(effect.clone());
+
+        let effect_scope = Scope(effect_id);
+        let (result, new_value) = with_scope(effect_scope, || {
+            effect_scope.track();
+            (effect.compute)(None)
+        });
+
+        // set new value
+        let mut value = effect.value.borrow_mut();
+        let value = value
+            .downcast_mut::<Option<T>>()
+            .expect("to downcast effect value");
+        *value = Some(new_value);
+
+        *runtime.current_effect.borrow_mut() = None;
+
+        result
+    });
+
+    result
+}
+
 /// Do a observer clean up at the beginning of each effect run. It clears the effect
 /// from all the Signals that this effect subscribes to, and clears all the signals
 /// that's stored in this effect, so that the next effect run can re-track signals.
@@ -171,3 +260,51 @@ where
         self.observers.borrow_mut().take()
     }
 }
+
+impl<T, I, C, U> EffectTrait for UpdaterEffect<T, I, C, U>
+where
+    T: 'static,
+    C: Fn(Option<T>) -> (I, T),
+    U: Fn(I, T) -> T,
+{
+    fn id(&self) -> Id {
+        self.id
+    }
+
+    fn run(&self) -> bool {
+        let curr_value = {
+            // downcast value
+            let mut value = self.value.borrow_mut();
+            let value = value
+                .downcast_mut::<Option<T>>()
+                .expect("to downcast effect value");
+            value.take()
+        };
+
+        // run the effect
+        let (i, t) = (self.compute)(curr_value);
+        let new_value = (self.on_change)(i, t);
+
+        // set new value
+        let mut value = self.value.borrow_mut();
+        let value = value
+            .downcast_mut::<Option<T>>()
+            .expect("to downcast effect value");
+        *value = Some(new_value);
+
+        true
+    }
+
+    fn add_observer(&self, id: Id) {
+        let mut observers = self.observers.borrow_mut();
+        if let Some(observers) = observers.as_mut() {
+            observers.insert(id);
+        } else {
+            *observers = Some(HashSet::from_iter([id]));
+        }
+    }
+
+    fn clear_observers(&self) -> Option<HashSet<Id>> {
+        self.observers.borrow_mut().take()
+    }
+}

reactive/src/lib.rs

@@ -8,7 +8,7 @@ mod signal;
 mod trigger;
 
 pub use context::{provide_context, use_context};
-pub use effect::{batch, create_effect, untrack};
+pub use effect::{batch, create_effect, create_stateful_updater, create_updater, untrack};
 pub use memo::{create_memo, Memo};
 pub use scope::{as_child_of_current_scope, with_scope, Scope};
 pub use signal::{create_rw_signal, create_signal, ReadSignal, RwSignal, WriteSignal};

reactive/src/scope.rs

@@ -115,7 +115,7 @@ impl Scope {
 }
 
 /// Runs the given code with the given Scope
-pub fn with_scope<T>(scope: Scope, f: impl FnOnce() -> T + 'static) -> T
+pub fn with_scope<T>(scope: Scope, f: impl FnOnce() -> T) -> T
 where
     T: 'static,
 {

src/views/dyn_container.rs

@@ -1,4 +1,4 @@
-use floem_reactive::{as_child_of_current_scope, create_effect, Scope};
+use floem_reactive::{as_child_of_current_scope, create_updater, Scope};
 
 use crate::{
     id::Id,
@@ -74,15 +74,16 @@ pub fn dyn_container<CF: Fn(T) -> Box<dyn View> + 'static, T: 'static>(
 ) -> DynamicContainer<T> {
     let id = Id::next();
 
-    create_effect(move |_| {
-        id.update_state(update_view(), false);
+    let initial = create_updater(update_view, move |new_state| {
+        id.update_state(new_state, false)
     });
 
     let child_fn = Box::new(as_child_of_current_scope(child_fn));
+    let (child, child_scope) = child_fn(initial);
     DynamicContainer {
         id,
-        child: Box::new(crate::views::empty()),
-        child_scope: Scope::new(),
+        child,
+        child_scope,
         child_fn,
     }
 }

src/views/label.rs

@@ -10,7 +10,7 @@ use crate::{
     unit::PxPct,
     view::View,
 };
-use floem_reactive::create_effect;
+use floem_reactive::create_updater;
 use floem_renderer::Renderer;
 use kurbo::{Point, Rect};
 use peniko::Color;
@@ -62,11 +62,11 @@ pub fn static_label(label: impl Into<String>) -> Label {
 
 pub fn label<S: Display + 'static>(label: impl Fn() -> S + 'static) -> Label {
     let id = Id::next();
-    create_effect(move |_| {
-        let new_label = label().to_string();
-        id.update_state(new_label, false);
-    });
-    Label::new(id, String::new())
+    let initial_label = create_updater(
+        move || label().to_string(),
+        move |new_label| id.update_state(new_label, false),
+    );
+    Label::new(id, initial_label)
 }
 
 impl Label {