Reduce the need for Send + Sync bounds on generics

crates/gpui2/src/action.rs

@@ -19,7 +19,7 @@ pub trait Action: Any + Send + Sync {
 
 impl<A> Action for A
 where
-    A: for<'a> Deserialize<'a> + Any + PartialEq + Clone + Default + Send + Sync,
+    A: for<'a> Deserialize<'a> + PartialEq + Any + Send + Sync + Clone + Default,
 {
     fn qualified_name() -> SharedString {
         type_name::<A>().into()

crates/gpui2/src/app.rs

@@ -22,7 +22,9 @@ use parking_lot::{Mutex, RwLock};
 use slotmap::SlotMap;
 use std::{
     any::{type_name, Any, TypeId},
+    marker::PhantomData,
     mem,
+    ops::{Deref, DerefMut},
     sync::{atomic::Ordering::SeqCst, Arc, Weak},
     time::Duration,
 };
@@ -178,7 +180,7 @@ pub struct AppContext {
     pub(crate) svg_renderer: SvgRenderer,
     pub(crate) image_cache: ImageCache,
     pub(crate) text_style_stack: Vec<TextStyleRefinement>,
-    pub(crate) globals_by_type: HashMap<TypeId, Box<dyn Any + Send + Sync>>,
+    pub(crate) globals_by_type: HashMap<TypeId, AnyBox>,
     pub(crate) unit_entity: Handle<()>,
     pub(crate) entities: EntityMap,
     pub(crate) windows: SlotMap<WindowId, Option<Window>>,
@@ -545,19 +547,16 @@ impl AppContext {
             .unwrap()
     }
 
-    pub fn set_global<T: Send + Sync + 'static>(&mut self, global: T) {
+    pub fn set_global<G: Any + Send + Sync>(&mut self, global: G) {
-        let global_type = TypeId::of::<T>();
+        let global_type = TypeId::of::<G>();
         self.push_effect(Effect::NotifyGlobalObservers { global_type });
         self.globals_by_type.insert(global_type, Box::new(global));
     }
 
-    pub fn update_global<G, R>(&mut self, f: impl FnOnce(&mut G, &mut Self) -> R) -> R
+    pub fn update_global<G: 'static, R>(&mut self, f: impl FnOnce(&mut G, &mut Self) -> R) -> R {
-    where
-        G: 'static + Send + Sync,
-    {
         let mut global = self.lease_global::<G>();
-        let result = f(global.as_mut(), self);
+        let result = f(&mut global, self);
-        self.restore_global(global);
+        self.end_global_lease(global);
         result
     }
 
@@ -574,19 +573,19 @@ impl AppContext {
         )
     }
 
-    pub(crate) fn lease_global<G: 'static + Send + Sync>(&mut self) -> Box<G> {
+    pub(crate) fn lease_global<G: 'static>(&mut self) -> GlobalLease<G> {
-        self.globals_by_type
+        GlobalLease::new(
-            .remove(&TypeId::of::<G>())
+            self.globals_by_type
-            .ok_or_else(|| anyhow!("no global registered of type {}", type_name::<G>()))
+                .remove(&TypeId::of::<G>())
-            .unwrap()
+                .ok_or_else(|| anyhow!("no global registered of type {}", type_name::<G>()))
-            .downcast()
+                .unwrap(),
-            .unwrap()
+        )
     }
 
-    pub(crate) fn restore_global<G: 'static + Send + Sync>(&mut self, global: Box<G>) {
+    pub(crate) fn end_global_lease<G: 'static>(&mut self, lease: GlobalLease<G>) {
         let global_type = TypeId::of::<G>();
         self.push_effect(Effect::NotifyGlobalObservers { global_type });
-        self.globals_by_type.insert(global_type, global);
+        self.globals_by_type.insert(global_type, lease.global);
     }
 
     pub(crate) fn push_text_style(&mut self, text_style: TextStyleRefinement) {
@@ -639,21 +638,21 @@ impl AppContext {
 }
 
 impl Context for AppContext {
-    type EntityContext<'a, 'w, T: Send + Sync + 'static> = ModelContext<'a, T>;
+    type EntityContext<'a, 'w, T> = ModelContext<'a, T>;
     type Result<T> = T;
 
-    fn entity<T: Send + Sync + 'static>(
+    fn entity<T: Any + Send + Sync>(
         &mut self,
         build_entity: impl FnOnce(&mut Self::EntityContext<'_, '_, T>) -> T,
     ) -> Handle<T> {
         self.update(|cx| {
             let slot = cx.entities.reserve();
-            let entity = build_entity(&mut ModelContext::mutable(cx, slot.entity_id));
+            let entity = build_entity(&mut ModelContext::mutable(cx, slot.downgrade()));
             cx.entities.insert(slot, entity)
         })
     }
 
-    fn update_entity<T: Send + Sync + 'static, R>(
+    fn update_entity<T: 'static, R>(
         &mut self,
         handle: &Handle<T>,
         update: impl FnOnce(&mut T, &mut Self::EntityContext<'_, '_, T>) -> R,
@@ -662,7 +661,7 @@ impl Context for AppContext {
             let mut entity = cx.entities.lease(handle);
             let result = update(
                 &mut entity,
-                &mut ModelContext::mutable(cx, handle.entity_id),
+                &mut ModelContext::mutable(cx, handle.downgrade()),
             );
             cx.entities.end_lease(entity);
             result
@@ -723,11 +722,11 @@ impl MainThread<AppContext> {
         self.platform().open_url(url);
     }
 
-    pub fn open_window<S: 'static + Send + Sync>(
+    pub fn open_window<V: 'static>(
         &mut self,
         options: crate::WindowOptions,
-        build_root_view: impl FnOnce(&mut WindowContext) -> View<S> + Send + 'static,
+        build_root_view: impl FnOnce(&mut WindowContext) -> View<V> + Send + 'static,
-    ) -> WindowHandle<S> {
+    ) -> WindowHandle<V> {
         self.update(|cx| {
             let id = cx.windows.insert(None);
             let handle = WindowHandle::new(id);
@@ -768,6 +767,34 @@ pub(crate) enum Effect {
     },
 }
 
+pub(crate) struct GlobalLease<G: 'static> {
+    global: AnyBox,
+    global_type: PhantomData<G>,
+}
+
+impl<G: 'static> GlobalLease<G> {
+    fn new(global: AnyBox) -> Self {
+        GlobalLease {
+            global,
+            global_type: PhantomData,
+        }
+    }
+}
+
+impl<G: 'static> Deref for GlobalLease<G> {
+    type Target = G;
+
+    fn deref(&self) -> &Self::Target {
+        self.global.downcast_ref().unwrap()
+    }
+}
+
+impl<G: 'static> DerefMut for GlobalLease<G> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.global.downcast_mut().unwrap()
+    }
+}
+
 pub(crate) struct AnyDrag {
     pub drag_handle_view: AnyView,
     pub cursor_offset: Point<Pixels>,

crates/gpui2/src/app/async_context.rs

@@ -5,7 +5,7 @@ use crate::{
 use anyhow::anyhow;
 use derive_more::{Deref, DerefMut};
 use parking_lot::Mutex;
-use std::{future::Future, sync::Weak};
+use std::{any::Any, future::Future, sync::Weak};
 
 #[derive(Clone)]
 pub struct AsyncAppContext {
@@ -14,13 +14,16 @@ pub struct AsyncAppContext {
 }
 
 impl Context for AsyncAppContext {
-    type EntityContext<'a, 'w, T: 'static + Send + Sync> = ModelContext<'a, T>;
+    type EntityContext<'a, 'w, T> = ModelContext<'a, T>;
     type Result<T> = Result<T>;
 
-    fn entity<T: Send + Sync + 'static>(
+    fn entity<T: 'static>(
         &mut self,
         build_entity: impl FnOnce(&mut Self::EntityContext<'_, '_, T>) -> T,
-    ) -> Self::Result<Handle<T>> {
+    ) -> Self::Result<Handle<T>>
+    where
+        T: Any + Send + Sync,
+    {
         let app = self
             .app
             .upgrade()
@@ -29,7 +32,7 @@ impl Context for AsyncAppContext {
         Ok(lock.entity(build_entity))
     }
 
-    fn update_entity<T: Send + Sync + 'static, R>(
+    fn update_entity<T: 'static, R>(
         &mut self,
         handle: &Handle<T>,
         update: impl FnOnce(&mut T, &mut Self::EntityContext<'_, '_, T>) -> R,
@@ -129,7 +132,7 @@ impl AsyncAppContext {
         Ok(app_context.run_on_main(f))
     }
 
-    pub fn has_global<G: 'static + Send + Sync>(&self) -> Result<bool> {
+    pub fn has_global<G: 'static>(&self) -> Result<bool> {
         let app = self
             .app
             .upgrade()
@@ -138,10 +141,7 @@ impl AsyncAppContext {
         Ok(lock.has_global::<G>())
     }
 
-    pub fn read_global<G: 'static + Send + Sync, R>(
+    pub fn read_global<G: 'static, R>(&self, read: impl FnOnce(&G, &AppContext) -> R) -> Result<R> {
-        &self,
-        read: impl FnOnce(&G, &AppContext) -> R,
-    ) -> Result<R> {
         let app = self
             .app
             .upgrade()
@@ -150,7 +150,7 @@ impl AsyncAppContext {
         Ok(read(lock.global(), &lock))
     }
 
-    pub fn try_read_global<G: 'static + Send + Sync, R>(
+    pub fn try_read_global<G: 'static, R>(
         &self,
         read: impl FnOnce(&G, &AppContext) -> R,
     ) -> Option<R> {
@@ -159,7 +159,7 @@ impl AsyncAppContext {
         Some(read(lock.try_global()?, &lock))
     }
 
-    pub fn update_global<G: 'static + Send + Sync, R>(
+    pub fn update_global<G: 'static, R>(
         &mut self,
         update: impl FnOnce(&mut G, &mut AppContext) -> R,
     ) -> Result<R> {
@@ -195,7 +195,7 @@ impl AsyncWindowContext {
             .ok();
     }
 
-    pub fn read_global<G: 'static + Send + Sync, R>(
+    pub fn read_global<G: 'static, R>(
         &self,
         read: impl FnOnce(&G, &WindowContext) -> R,
     ) -> Result<R> {
@@ -203,28 +203,34 @@ impl AsyncWindowContext {
             .read_window(self.window, |cx| read(cx.global(), cx))
     }
 
-    pub fn update_global<G: 'static + Send + Sync, R>(
+    pub fn update_global<G, R>(
         &mut self,
         update: impl FnOnce(&mut G, &mut WindowContext) -> R,
-    ) -> Result<R> {
+    ) -> Result<R>
+    where
+        G: 'static,
+    {
         self.app
             .update_window(self.window, |cx| cx.update_global(update))
     }
 }
 
 impl Context for AsyncWindowContext {
-    type EntityContext<'a, 'w, T: 'static + Send + Sync> = ViewContext<'a, 'w, T>;
+    type EntityContext<'a, 'w, T> = ViewContext<'a, 'w, T>;
     type Result<T> = Result<T>;
 
-    fn entity<R: Send + Sync + 'static>(
+    fn entity<T>(
         &mut self,
-        build_entity: impl FnOnce(&mut Self::EntityContext<'_, '_, R>) -> R,
+        build_entity: impl FnOnce(&mut Self::EntityContext<'_, '_, T>) -> T,
-    ) -> Result<Handle<R>> {
+    ) -> Result<Handle<T>>
+    where
+        T: Any + Send + Sync,
+    {
         self.app
             .update_window(self.window, |cx| cx.entity(build_entity))
     }
 
-    fn update_entity<T: Send + Sync + 'static, R>(
+    fn update_entity<T: 'static, R>(
         &mut self,
         handle: &Handle<T>,
         update: impl FnOnce(&mut T, &mut Self::EntityContext<'_, '_, T>) -> R,
@@ -233,3 +239,14 @@ impl Context for AsyncWindowContext {
             .update_window(self.window, |cx| cx.update_entity(handle, update))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_async_app_context_send_sync() {
+        fn assert_send_sync<T: Send + Sync>() {}
+        assert_send_sync::<AsyncAppContext>();
+    }
+}

crates/gpui2/src/app/entity_map.rs

@@ -1,4 +1,4 @@
-use crate::{AppContext, Context};
+use crate::{AnyBox, AppContext, Context};
 use anyhow::{anyhow, Result};
 use derive_more::{Deref, DerefMut};
 use parking_lot::{RwLock, RwLockUpgradableReadGuard};
@@ -30,7 +30,7 @@ impl Display for EntityId {
 }
 
 pub(crate) struct EntityMap {
-    entities: SecondaryMap<EntityId, Box<dyn Any + Send + Sync>>,
+    entities: SecondaryMap<EntityId, AnyBox>,
     ref_counts: Arc<RwLock<EntityRefCounts>>,
 }
 
@@ -51,56 +51,46 @@ impl EntityMap {
     }
 
     /// Reserve a slot for an entity, which you can subsequently use with `insert`.
-    pub fn reserve<T: 'static + Send + Sync>(&self) -> Slot<T> {
+    pub fn reserve<T: 'static>(&self) -> Slot<T> {
         let id = self.ref_counts.write().counts.insert(1.into());
         Slot(Handle::new(id, Arc::downgrade(&self.ref_counts)))
     }
 
     /// Insert an entity into a slot obtained by calling `reserve`.
-    pub fn insert<T: 'static + Any + Send + Sync>(
+    pub fn insert<T>(&mut self, slot: Slot<T>, entity: T) -> Handle<T>
-        &mut self,
+    where
-        slot: Slot<T>,
+        T: Any + Send + Sync,
-        entity: T,
+    {
-    ) -> Handle<T> {
         let handle = slot.0;
         self.entities.insert(handle.entity_id, Box::new(entity));
         handle
     }
 
     /// Move an entity to the stack.
-    pub fn lease<'a, T: 'static + Send + Sync>(&mut self, handle: &'a Handle<T>) -> Lease<'a, T> {
+    pub fn lease<'a, T>(&mut self, handle: &'a Handle<T>) -> Lease<'a, T> {
         let entity = Some(
             self.entities
                 .remove(handle.entity_id)
-                .expect("Circular entity lease. Is the entity already being updated?")
+                .expect("Circular entity lease. Is the entity already being updated?"),
-                .downcast::<T>()
-                .unwrap(),
         );
-        Lease { handle, entity }
+        Lease {
-    }
+            handle,
-
+            entity,
-    /// Return an entity after moving it to the stack.
-    pub fn end_lease<T: 'static + Send + Sync>(&mut self, mut lease: Lease<T>) {
-        self.entities
-            .insert(lease.handle.entity_id, lease.entity.take().unwrap());
-    }
-
-    pub fn read<T: 'static + Send + Sync>(&self, handle: &Handle<T>) -> &T {
-        self.entities[handle.entity_id].downcast_ref().unwrap()
-    }
-
-    pub fn weak_handle<T: 'static + Send + Sync>(&self, id: EntityId) -> WeakHandle<T> {
-        WeakHandle {
-            any_handle: AnyWeakHandle {
-                entity_id: id,
-                entity_type: TypeId::of::<T>(),
-                entity_ref_counts: Arc::downgrade(&self.ref_counts),
-            },
             entity_type: PhantomData,
         }
     }
 
-    pub fn take_dropped(&mut self) -> Vec<(EntityId, Box<dyn Any + Send + Sync>)> {
+    /// Return an entity after moving it to the stack.
+    pub fn end_lease<T>(&mut self, mut lease: Lease<T>) {
+        self.entities
+            .insert(lease.handle.entity_id, lease.entity.take().unwrap());
+    }
+
+    pub fn read<T>(&self, handle: &Handle<T>) -> &T {
+        (handle.downcast_entity)(&self.entities[handle.entity_id])
+    }
+
+    pub fn take_dropped(&mut self) -> Vec<(EntityId, AnyBox)> {
         let dropped_entity_ids = mem::take(&mut self.ref_counts.write().dropped_entity_ids);
         dropped_entity_ids
             .into_iter()
@@ -109,35 +99,27 @@ impl EntityMap {
     }
 }
 
-pub struct Lease<'a, T: Send + Sync> {
+pub struct Lease<'a, T> {
-    entity: Option<Box<T>>,
+    entity: Option<AnyBox>,
     pub handle: &'a Handle<T>,
+    entity_type: PhantomData<T>,
 }
 
-impl<'a, T> core::ops::Deref for Lease<'a, T>
+impl<'a, T> core::ops::Deref for Lease<'a, T> {
-where
-    T: Send + Sync,
-{
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
-        self.entity.as_ref().unwrap()
+        (self.handle.downcast_entity)(self.entity.as_ref().unwrap())
     }
 }
 
-impl<'a, T> core::ops::DerefMut for Lease<'a, T>
+impl<'a, T> core::ops::DerefMut for Lease<'a, T> {
-where
-    T: Send + Sync,
-{
     fn deref_mut(&mut self) -> &mut Self::Target {
-        self.entity.as_mut().unwrap()
+        (self.handle.downcast_entity_mut)(self.entity.as_mut().unwrap())
     }
 }
 
-impl<'a, T> Drop for Lease<'a, T>
+impl<'a, T> Drop for Lease<'a, T> {
-where
-    T: Send + Sync,
-{
     fn drop(&mut self) {
         if self.entity.is_some() {
             // We don't panic here, because other panics can cause us to drop the lease without ending it cleanly.
@@ -147,7 +129,7 @@ where
 }
 
 #[derive(Deref, DerefMut)]
-pub struct Slot<T: Send + Sync + 'static>(Handle<T>);
+pub struct Slot<T>(Handle<T>);
 
 pub struct AnyHandle {
     pub(crate) entity_id: EntityId,
@@ -176,14 +158,13 @@ impl AnyHandle {
         }
     }
 
-    pub fn downcast<T>(&self) -> Option<Handle<T>>
+    pub fn downcast<T: 'static>(&self) -> Option<Handle<T>> {
-    where
-        T: 'static + Send + Sync,
-    {
         if TypeId::of::<T>() == self.entity_type {
             Some(Handle {
                 any_handle: self.clone(),
                 entity_type: PhantomData,
+                downcast_entity: |any| any.downcast_ref().unwrap(),
+                downcast_entity_mut: |any| any.downcast_mut().unwrap(),
             })
         } else {
             None
@@ -231,10 +212,7 @@ impl Drop for AnyHandle {
     }
 }
 
-impl<T> From<Handle<T>> for AnyHandle
+impl<T> From<Handle<T>> for AnyHandle {
-where
-    T: 'static + Send + Sync,
-{
     fn from(handle: Handle<T>) -> Self {
         handle.any_handle
     }
@@ -255,18 +233,28 @@ impl PartialEq for AnyHandle {
 impl Eq for AnyHandle {}
 
 #[derive(Deref, DerefMut)]
-pub struct Handle<T: Send + Sync> {
+pub struct Handle<T> {
     #[deref]
     #[deref_mut]
     any_handle: AnyHandle,
     entity_type: PhantomData<T>,
+    downcast_entity: fn(&dyn Any) -> &T,
+    downcast_entity_mut: fn(&mut dyn Any) -> &mut T,
 }
 
-impl<T: 'static + Send + Sync> Handle<T> {
+unsafe impl<T> Send for Handle<T> {}
-    fn new(id: EntityId, entity_map: Weak<RwLock<EntityRefCounts>>) -> Self {
+unsafe impl<T> Sync for Handle<T> {}
+
+impl<T: 'static> Handle<T> {
+    fn new(id: EntityId, entity_map: Weak<RwLock<EntityRefCounts>>) -> Self
+    where
+        T: 'static,
+    {
         Self {
             any_handle: AnyHandle::new(id, TypeId::of::<T>(), entity_map),
             entity_type: PhantomData,
+            downcast_entity: |any| any.downcast_ref().unwrap(),
+            downcast_entity_mut: |any| any.downcast_mut().unwrap(),
         }
     }
 
@@ -274,6 +262,8 @@ impl<T: 'static + Send + Sync> Handle<T> {
         WeakHandle {
             any_handle: self.any_handle.downgrade(),
             entity_type: self.entity_type,
+            downcast_entity: self.downcast_entity,
+            downcast_entity_mut: self.downcast_entity_mut,
         }
     }
 
@@ -286,25 +276,30 @@ impl<T: 'static + Send + Sync> Handle<T> {
     /// The update function receives a context appropriate for its environment.
     /// When updating in an `AppContext`, it receives a `ModelContext`.
     /// When updating an a `WindowContext`, it receives a `ViewContext`.
-    pub fn update<C: Context, R>(
+    pub fn update<C, R>(
         &self,
         cx: &mut C,
         update: impl FnOnce(&mut T, &mut C::EntityContext<'_, '_, T>) -> R,
-    ) -> C::Result<R> {
+    ) -> C::Result<R>
+    where
+        C: Context,
+    {
         cx.update_entity(self, update)
     }
 }
 
-impl<T: Send + Sync> Clone for Handle<T> {
+impl<T> Clone for Handle<T> {
     fn clone(&self) -> Self {
         Self {
             any_handle: self.any_handle.clone(),
             entity_type: self.entity_type,
+            downcast_entity: self.downcast_entity,
+            downcast_entity_mut: self.downcast_entity_mut,
         }
     }
 }
 
-impl<T: 'static + Send + Sync> std::fmt::Debug for Handle<T> {
+impl<T> std::fmt::Debug for Handle<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(
             f,
@@ -315,19 +310,19 @@ impl<T: 'static + Send + Sync> std::fmt::Debug for Handle<T> {
     }
 }
 
-impl<T: Send + Sync + 'static> Hash for Handle<T> {
+impl<T> Hash for Handle<T> {
     fn hash<H: Hasher>(&self, state: &mut H) {
         self.any_handle.hash(state);
     }
 }
 
-impl<T: Send + Sync + 'static> PartialEq for Handle<T> {
+impl<T> PartialEq for Handle<T> {
     fn eq(&self, other: &Self) -> bool {
         self.any_handle == other.any_handle
     }
 }
 
-impl<T: Send + Sync + 'static> Eq for Handle<T> {}
+impl<T> Eq for Handle<T> {}
 
 #[derive(Clone)]
 pub struct AnyWeakHandle {
@@ -365,10 +360,7 @@ impl AnyWeakHandle {
     }
 }
 
-impl<T> From<WeakHandle<T>> for AnyWeakHandle
+impl<T> From<WeakHandle<T>> for AnyWeakHandle {
-where
-    T: 'static + Send + Sync,
-{
     fn from(handle: WeakHandle<T>) -> Self {
         handle.any_handle
     }
@@ -394,22 +386,31 @@ pub struct WeakHandle<T> {
     #[deref_mut]
     any_handle: AnyWeakHandle,
     entity_type: PhantomData<T>,
+    downcast_entity: fn(&dyn Any) -> &T,
+    pub(crate) downcast_entity_mut: fn(&mut dyn Any) -> &mut T,
 }
 
-impl<T: 'static + Send + Sync> Clone for WeakHandle<T> {
+unsafe impl<T> Send for WeakHandle<T> {}
+unsafe impl<T> Sync for WeakHandle<T> {}
+
+impl<T> Clone for WeakHandle<T> {
     fn clone(&self) -> Self {
         Self {
             any_handle: self.any_handle.clone(),
             entity_type: self.entity_type,
+            downcast_entity: self.downcast_entity,
+            downcast_entity_mut: self.downcast_entity_mut,
         }
     }
 }
 
-impl<T: Send + Sync + 'static> WeakHandle<T> {
+impl<T: 'static> WeakHandle<T> {
     pub fn upgrade(&self) -> Option<Handle<T>> {
         Some(Handle {
             any_handle: self.any_handle.upgrade()?,
             entity_type: self.entity_type,
+            downcast_entity: self.downcast_entity,
+            downcast_entity_mut: self.downcast_entity_mut,
         })
     }
 
@@ -420,12 +421,13 @@ impl<T: Send + Sync + 'static> WeakHandle<T> {
     /// The update function receives a context appropriate for its environment.
     /// When updating in an `AppContext`, it receives a `ModelContext`.
     /// When updating an a `WindowContext`, it receives a `ViewContext`.
-    pub fn update<C: Context, R>(
+    pub fn update<C, R>(
         &self,
         cx: &mut C,
         update: impl FnOnce(&mut T, &mut C::EntityContext<'_, '_, T>) -> R,
     ) -> Result<R>
     where
+        C: Context,
         Result<C::Result<R>>: crate::Flatten<R>,
     {
         crate::Flatten::flatten(
@@ -436,16 +438,16 @@ impl<T: Send + Sync + 'static> WeakHandle<T> {
     }
 }
 
-impl<T: Send + Sync + 'static> Hash for WeakHandle<T> {
+impl<T> Hash for WeakHandle<T> {
     fn hash<H: Hasher>(&self, state: &mut H) {
         self.any_handle.hash(state);
     }
 }
 
-impl<T: Send + Sync + 'static> PartialEq for WeakHandle<T> {
+impl<T> PartialEq for WeakHandle<T> {
     fn eq(&self, other: &Self) -> bool {
         self.any_handle == other.any_handle
     }
 }
 
-impl<T: Send + Sync + 'static> Eq for WeakHandle<T> {}
+impl<T> Eq for WeakHandle<T> {}

crates/gpui2/src/app/model_context.rs

@@ -4,28 +4,29 @@ use crate::{
 };
 use derive_more::{Deref, DerefMut};
 use futures::FutureExt;
-use std::{any::TypeId, future::Future, marker::PhantomData};
+use std::{
+    any::{Any, TypeId},
+    future::Future,
+};
 
 #[derive(Deref, DerefMut)]
 pub struct ModelContext<'a, T> {
     #[deref]
     #[deref_mut]
     app: Reference<'a, AppContext>,
-    entity_type: PhantomData<T>,
+    model_state: WeakHandle<T>,
-    entity_id: EntityId,
 }
 
-impl<'a, T: Send + Sync + 'static> ModelContext<'a, T> {
+impl<'a, T: 'static> ModelContext<'a, T> {
-    pub(crate) fn mutable(app: &'a mut AppContext, entity_id: EntityId) -> Self {
+    pub(crate) fn mutable(app: &'a mut AppContext, model_state: WeakHandle<T>) -> Self {
         Self {
             app: Reference::Mutable(app),
-            entity_type: PhantomData,
+            model_state,
-            entity_id,
         }
     }
 
     pub fn entity_id(&self) -> EntityId {
-        self.entity_id
+        self.model_state.entity_id
     }
 
     pub fn handle(&self) -> Handle<T> {
@@ -35,14 +36,17 @@ impl<'a, T: Send + Sync + 'static> ModelContext<'a, T> {
     }
 
     pub fn weak_handle(&self) -> WeakHandle<T> {
-        self.app.entities.weak_handle(self.entity_id)
+        self.model_state.clone()
     }
 
-    pub fn observe<E: Send + Sync + 'static>(
+    pub fn observe<T2: 'static>(
         &mut self,
-        handle: &Handle<E>,
+        handle: &Handle<T2>,
-        on_notify: impl Fn(&mut T, Handle<E>, &mut ModelContext<'_, T>) + Send + Sync + 'static,
+        on_notify: impl Fn(&mut T, Handle<T2>, &mut ModelContext<'_, T>) + Send + Sync + 'static,
-    ) -> Subscription {
+    ) -> Subscription
+    where
+        T: Any + Send + Sync,
+    {
         let this = self.weak_handle();
         let handle = handle.downgrade();
         self.app.observers.insert(
@@ -58,14 +62,17 @@ impl<'a, T: Send + Sync + 'static> ModelContext<'a, T> {
         )
     }
 
-    pub fn subscribe<E: EventEmitter + Send + Sync + 'static>(
+    pub fn subscribe<E: 'static + EventEmitter>(
         &mut self,
         handle: &Handle<E>,
         on_event: impl Fn(&mut T, Handle<E>, &E::Event, &mut ModelContext<'_, T>)
             + Send
             + Sync
             + 'static,
-    ) -> Subscription {
+    ) -> Subscription
+    where
+        T: Any + Send + Sync,
+    {
         let this = self.weak_handle();
         let handle = handle.downgrade();
         self.app.event_listeners.insert(
@@ -85,9 +92,12 @@ impl<'a, T: Send + Sync + 'static> ModelContext<'a, T> {
     pub fn on_release(
         &mut self,
         on_release: impl Fn(&mut T, &mut AppContext) + Send + Sync + 'static,
-    ) -> Subscription {
+    ) -> Subscription
+    where
+        T: 'static,
+    {
         self.app.release_listeners.insert(
-            self.entity_id,
+            self.model_state.entity_id,
             Box::new(move |this, cx| {
                 let this = this.downcast_mut().expect("invalid entity type");
                 on_release(this, cx);
@@ -95,11 +105,14 @@ impl<'a, T: Send + Sync + 'static> ModelContext<'a, T> {
         )
     }
 
-    pub fn observe_release<E: Send + Sync + 'static>(
+    pub fn observe_release<E: 'static>(
         &mut self,
         handle: &Handle<E>,
         on_release: impl Fn(&mut T, &mut E, &mut ModelContext<'_, T>) + Send + Sync + 'static,
-    ) -> Subscription {
+    ) -> Subscription
+    where
+        T: Any + Send + Sync,
+    {
         let this = self.weak_handle();
         self.app.release_listeners.insert(
             handle.entity_id,
@@ -115,7 +128,10 @@ impl<'a, T: Send + Sync + 'static> ModelContext<'a, T> {
     pub fn observe_global<G: 'static>(
         &mut self,
         f: impl Fn(&mut T, &mut ModelContext<'_, T>) + Send + Sync + 'static,
-    ) -> Subscription {
+    ) -> Subscription
+    where
+        T: Any + Send + Sync,
+    {
         let handle = self.weak_handle();
         self.global_observers.insert(
             TypeId::of::<G>(),
@@ -129,6 +145,7 @@ impl<'a, T: Send + Sync + 'static> ModelContext<'a, T> {
     ) -> Subscription
     where
         Fut: 'static + Future<Output = ()> + Send,
+        T: Any + Send + Sync,
     {
         let handle = self.weak_handle();
         self.app.quit_observers.insert(
@@ -146,9 +163,13 @@ impl<'a, T: Send + Sync + 'static> ModelContext<'a, T> {
     }
 
     pub fn notify(&mut self) {
-        if self.app.pending_notifications.insert(self.entity_id) {
+        if self
+            .app
+            .pending_notifications
+            .insert(self.model_state.entity_id)
+        {
             self.app.pending_effects.push_back(Effect::Notify {
-                emitter: self.entity_id,
+                emitter: self.model_state.entity_id,
             });
         }
     }
@@ -158,8 +179,8 @@ impl<'a, T: Send + Sync + 'static> ModelContext<'a, T> {
         G: 'static + Send + Sync,
     {
         let mut global = self.app.lease_global::<G>();
-        let result = f(global.as_mut(), self);
+        let result = f(&mut global, self);
-        self.app.restore_global(global);
+        self.app.end_global_lease(global);
         result
     }
 
@@ -168,6 +189,7 @@ impl<'a, T: Send + Sync + 'static> ModelContext<'a, T> {
         f: impl FnOnce(WeakHandle<T>, AsyncAppContext) -> Fut + Send + 'static,
     ) -> Task<R>
     where
+        T: 'static,
         Fut: Future<Output = R> + Send + 'static,
         R: Send + 'static,
     {
@@ -176,27 +198,34 @@ impl<'a, T: Send + Sync + 'static> ModelContext<'a, T> {
     }
 }
 
-impl<'a, T: EventEmitter + Send + Sync + 'static> ModelContext<'a, T> {
+impl<'a, T> ModelContext<'a, T>
+where
+    T: EventEmitter,
+    T::Event: Send + Sync,
+{
     pub fn emit(&mut self, event: T::Event) {
         self.app.pending_effects.push_back(Effect::Emit {
-            emitter: self.entity_id,
+            emitter: self.model_state.entity_id,
             event: Box::new(event),
         });
     }
 }
 
-impl<'a, T: 'static> Context for ModelContext<'a, T> {
+impl<'a, T> Context for ModelContext<'a, T> {
-    type EntityContext<'b, 'c, U: Send + Sync + 'static> = ModelContext<'b, U>;
+    type EntityContext<'b, 'c, U> = ModelContext<'b, U>;
     type Result<U> = U;
 
-    fn entity<U: Send + Sync + 'static>(
+    fn entity<U>(
         &mut self,
         build_entity: impl FnOnce(&mut Self::EntityContext<'_, '_, U>) -> U,
-    ) -> Handle<U> {
+    ) -> Handle<U>
+    where
+        U: 'static + Send + Sync,
+    {
         self.app.entity(build_entity)
     }
 
-    fn update_entity<U: Send + Sync + 'static, R>(
+    fn update_entity<U: 'static, R>(
         &mut self,
         handle: &Handle<U>,
         update: impl FnOnce(&mut U, &mut Self::EntityContext<'_, '_, U>) -> R,

crates/gpui2/src/element.rs

@@ -1,11 +1,11 @@
 use crate::{BorrowWindow, Bounds, ElementId, LayoutId, Pixels, ViewContext};
 use derive_more::{Deref, DerefMut};
 pub(crate) use smallvec::SmallVec;
-use std::mem;
+use std::{any::Any, mem};
 
-pub trait Element: 'static + Send + Sync + IntoAnyElement<Self::ViewState> {
+pub trait Element: IntoAnyElement<Self::ViewState> {
-    type ViewState: 'static + Send + Sync;
+    type ViewState: 'static;
-    type ElementState: 'static + Send + Sync;
+    type ElementState: 'static;
 
     fn id(&self) -> Option<ElementId>;
 
@@ -15,6 +15,8 @@ pub trait Element: 'static + Send + Sync + IntoAnyElement<Self::ViewState> {
         element_state: Option<Self::ElementState>,
         cx: &mut ViewContext<Self::ViewState>,
     ) -> Self::ElementState;
+    // where
+    //     Self::ViewState: Any + Send + Sync;
 
     fn layout(
         &mut self,
@@ -22,6 +24,8 @@ pub trait Element: 'static + Send + Sync + IntoAnyElement<Self::ViewState> {
         element_state: &mut Self::ElementState,
         cx: &mut ViewContext<Self::ViewState>,
     ) -> LayoutId;
+    // where
+    //     Self::ViewState: Any + Send + Sync;
 
     fn paint(
         &mut self,
@@ -30,6 +34,9 @@ pub trait Element: 'static + Send + Sync + IntoAnyElement<Self::ViewState> {
         element_state: &mut Self::ElementState,
         cx: &mut ViewContext<Self::ViewState>,
     );
+
+    // where
+    //     Self::ViewState: Any + Send + Sync;
 }
 
 #[derive(Deref, DerefMut, Default, Clone, Debug, Eq, PartialEq, Hash)]
@@ -59,7 +66,7 @@ pub trait ParentElement: Element {
     }
 }
 
-trait ElementObject<V>: 'static + Send + Sync {
+trait ElementObject<V> {
     fn initialize(&mut self, view_state: &mut V, cx: &mut ViewContext<V>);
     fn layout(&mut self, view_state: &mut V, cx: &mut ViewContext<V>) -> LayoutId;
     fn paint(&mut self, view_state: &mut V, cx: &mut ViewContext<V>);
@@ -99,6 +106,8 @@ impl<E: Element> RenderedElement<E> {
 impl<E> ElementObject<E::ViewState> for RenderedElement<E>
 where
     E: Element,
+    // E::ViewState: Any + Send + Sync,
+    E::ElementState: Any + Send + Sync,
 {
     fn initialize(&mut self, view_state: &mut E::ViewState, cx: &mut ViewContext<E::ViewState>) {
         let frame_state = if let Some(id) = self.element.id() {
@@ -171,10 +180,15 @@ where
     }
 }
 
-pub struct AnyElement<V>(Box<dyn ElementObject<V>>);
+pub struct AnyElement<V>(Box<dyn ElementObject<V> + Send + Sync>);
 
-impl<V: 'static + Send + Sync> AnyElement<V> {
+impl<V> AnyElement<V> {
-    pub fn new<E: Element<ViewState = V>>(element: E) -> Self {
+    pub fn new<E>(element: E) -> Self
+    where
+        E: 'static + Send + Sync,
+        E: Element<ViewState = V>,
+        E::ElementState: Any + Send + Sync,
+    {
         AnyElement(Box::new(RenderedElement::new(element)))
     }
 

crates/gpui2/src/elements/div.rs

@@ -9,7 +9,7 @@ use refineable::Refineable;
 use smallvec::SmallVec;
 
 pub struct Div<
-    V: 'static + Send + Sync,
+    V: 'static,
     I: ElementInteraction<V> = StatelessInteraction<V>,
     F: ElementFocus<V> = FocusDisabled,
 > {
@@ -20,10 +20,7 @@ pub struct Div<
     base_style: StyleRefinement,
 }
 
-pub fn div<V>() -> Div<V, StatelessInteraction<V>, FocusDisabled>
+pub fn div<V: 'static>() -> Div<V, StatelessInteraction<V>, FocusDisabled> {
-where
-    V: 'static + Send + Sync,
-{
     Div {
         interaction: StatelessInteraction::default(),
         focus: FocusDisabled,
@@ -35,8 +32,8 @@ where
 
 impl<V, F> Div<V, StatelessInteraction<V>, F>
 where
+    V: 'static,
     F: ElementFocus<V>,
-    V: 'static + Send + Sync,
 {
     pub fn id(self, id: impl Into<ElementId>) -> Div<V, StatefulInteraction<V>, F> {
         Div {
@@ -53,7 +50,6 @@ impl<V, I, F> Div<V, I, F>
 where
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
-    V: 'static + Send + Sync,
 {
     pub fn group(mut self, group: impl Into<SharedString>) -> Self {
         self.group = Some(group.into());
@@ -108,10 +104,7 @@ where
     }
 }
 
-impl<V> Div<V, StatefulInteraction<V>, FocusDisabled>
+impl<V: 'static> Div<V, StatefulInteraction<V>, FocusDisabled> {
-where
-    V: 'static + Send + Sync,
-{
     pub fn focusable(self) -> Div<V, StatefulInteraction<V>, FocusEnabled<V>> {
         Div {
             interaction: self.interaction,
@@ -152,10 +145,7 @@ where
     }
 }
 
-impl<V> Div<V, StatelessInteraction<V>, FocusDisabled>
+impl<V: 'static> Div<V, StatelessInteraction<V>, FocusDisabled> {
-where
-    V: 'static + Send + Sync,
-{
     pub fn track_focus(
         self,
         handle: &FocusHandle,
@@ -172,8 +162,8 @@ where
 
 impl<V, I> Focusable for Div<V, I, FocusEnabled<V>>
 where
+    V: 'static,
     I: ElementInteraction<V>,
-    V: 'static + Send + Sync,
 {
     fn focus_listeners(&mut self) -> &mut FocusListeners<V> {
         &mut self.focus.focus_listeners
@@ -203,7 +193,6 @@ impl<V, I, F> Element for Div<V, I, F>
 where
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
-    V: 'static + Send + Sync,
 {
     type ViewState = V;
     type ElementState = DivState;
@@ -317,9 +306,9 @@ where
 
 impl<V, I, F> IntoAnyElement<V> for Div<V, I, F>
 where
+    // V: Any + Send + Sync,
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
-    V: 'static + Send + Sync,
 {
     fn into_any(self) -> AnyElement<V> {
         AnyElement::new(self)
@@ -330,7 +319,6 @@ impl<V, I, F> ParentElement for Div<V, I, F>
 where
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
-    V: 'static + Send + Sync,
 {
     fn children_mut(&mut self) -> &mut SmallVec<[AnyElement<Self::ViewState>; 2]> {
         &mut self.children
@@ -341,7 +329,6 @@ impl<V, I, F> Styled for Div<V, I, F>
 where
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
-    V: 'static + Send + Sync,
 {
     fn style(&mut self) -> &mut StyleRefinement {
         &mut self.base_style
@@ -352,7 +339,6 @@ impl<V, I, F> StatelessInteractive for Div<V, I, F>
 where
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
-    V: 'static + Send + Sync,
 {
     fn stateless_interaction(&mut self) -> &mut StatelessInteraction<V> {
         self.interaction.as_stateless_mut()
@@ -362,7 +348,6 @@ where
 impl<V, F> StatefulInteractive for Div<V, StatefulInteraction<V>, F>
 where
     F: ElementFocus<V>,
-    V: 'static + Send + Sync,
 {
     fn stateful_interaction(&mut self) -> &mut StatefulInteraction<Self::ViewState> {
         &mut self.interaction

crates/gpui2/src/elements/img.rs

@@ -8,7 +8,7 @@ use futures::FutureExt;
 use util::ResultExt;
 
 pub struct Img<
-    V: 'static + Send + Sync,
+    V: 'static,
     I: ElementInteraction<V> = StatelessInteraction<V>,
     F: ElementFocus<V> = FocusDisabled,
 > {
@@ -17,10 +17,7 @@ pub struct Img<
     grayscale: bool,
 }
 
-pub fn img<V>() -> Img<V, StatelessInteraction<V>, FocusDisabled>
+pub fn img<V: 'static>() -> Img<V, StatelessInteraction<V>, FocusDisabled> {
-where
-    V: 'static + Send + Sync,
-{
     Img {
         base: div(),
         uri: None,
@@ -30,7 +27,7 @@ where
 
 impl<V, I, F> Img<V, I, F>
 where
-    V: 'static + Send + Sync,
+    V: 'static,
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
 {
@@ -47,7 +44,6 @@ where
 
 impl<V, F> Img<V, StatelessInteraction<V>, F>
 where
-    V: 'static + Send + Sync,
     F: ElementFocus<V>,
 {
     pub fn id(self, id: impl Into<ElementId>) -> Img<V, StatefulInteraction<V>, F> {
@@ -61,7 +57,6 @@ where
 
 impl<V, I, F> IntoAnyElement<V> for Img<V, I, F>
 where
-    V: 'static + Send + Sync,
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
 {
@@ -72,7 +67,6 @@ where
 
 impl<V, I, F> Element for Img<V, I, F>
 where
-    V: Send + Sync + 'static,
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
 {
@@ -141,7 +135,6 @@ where
 
 impl<V, I, F> Styled for Img<V, I, F>
 where
-    V: 'static + Send + Sync,
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
 {
@@ -152,7 +145,6 @@ where
 
 impl<V, I, F> StatelessInteractive for Img<V, I, F>
 where
-    V: 'static + Send + Sync,
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
 {
@@ -163,7 +155,6 @@ where
 
 impl<V, F> StatefulInteractive for Img<V, StatefulInteraction<V>, F>
 where
-    V: 'static + Send + Sync,
     F: ElementFocus<V>,
 {
     fn stateful_interaction(&mut self) -> &mut StatefulInteraction<Self::ViewState> {
@@ -173,7 +164,7 @@ where
 
 impl<V, I> Focusable for Img<V, I, FocusEnabled<V>>
 where
-    V: 'static + Send + Sync,
+    V: 'static,
     I: ElementInteraction<V>,
 {
     fn focus_listeners(&mut self) -> &mut FocusListeners<Self::ViewState> {

crates/gpui2/src/elements/svg.rs

@@ -7,7 +7,7 @@ use crate::{
 use util::ResultExt;
 
 pub struct Svg<
-    V: 'static + Send + Sync,
+    V: 'static,
     I: ElementInteraction<V> = StatelessInteraction<V>,
     F: ElementFocus<V> = FocusDisabled,
 > {
@@ -15,10 +15,7 @@ pub struct Svg<
     path: Option<SharedString>,
 }
 
-pub fn svg<V>() -> Svg<V, StatelessInteraction<V>, FocusDisabled>
+pub fn svg<V: 'static>() -> Svg<V, StatelessInteraction<V>, FocusDisabled> {
-where
-    V: 'static + Send + Sync,
-{
     Svg {
         base: div(),
         path: None,
@@ -27,7 +24,6 @@ where
 
 impl<V, I, F> Svg<V, I, F>
 where
-    V: 'static + Send + Sync,
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
 {
@@ -39,7 +35,6 @@ where
 
 impl<V, F> Svg<V, StatelessInteraction<V>, F>
 where
-    V: 'static + Send + Sync,
     F: ElementFocus<V>,
 {
     pub fn id(self, id: impl Into<ElementId>) -> Svg<V, StatefulInteraction<V>, F> {
@@ -52,7 +47,6 @@ where
 
 impl<V, I, F> IntoAnyElement<V> for Svg<V, I, F>
 where
-    V: 'static + Send + Sync,
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
 {
@@ -63,7 +57,6 @@ where
 
 impl<V, I, F> Element for Svg<V, I, F>
 where
-    V: 'static + Send + Sync,
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
 {
@@ -115,7 +108,6 @@ where
 
 impl<V, I, F> Styled for Svg<V, I, F>
 where
-    V: 'static + Send + Sync,
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
 {
@@ -126,7 +118,6 @@ where
 
 impl<V, I, F> StatelessInteractive for Svg<V, I, F>
 where
-    V: 'static + Send + Sync,
     I: ElementInteraction<V>,
     F: ElementFocus<V>,
 {
@@ -137,7 +128,7 @@ where
 
 impl<V, F> StatefulInteractive for Svg<V, StatefulInteraction<V>, F>
 where
-    V: 'static + Send + Sync,
+    V: 'static,
     F: ElementFocus<V>,
 {
     fn stateful_interaction(&mut self) -> &mut StatefulInteraction<Self::ViewState> {
@@ -145,9 +136,8 @@ where
     }
 }
 
-impl<V, I> Focusable for Svg<V, I, FocusEnabled<V>>
+impl<V: 'static, I> Focusable for Svg<V, I, FocusEnabled<V>>
 where
-    V: 'static + Send + Sync,
     I: ElementInteraction<V>,
 {
     fn focus_listeners(&mut self) -> &mut FocusListeners<Self::ViewState> {

crates/gpui2/src/elements/text.rs

@@ -7,8 +7,8 @@ use smallvec::SmallVec;
 use std::{marker::PhantomData, sync::Arc};
 use util::ResultExt;
 
-impl<S: 'static + Send + Sync> IntoAnyElement<S> for SharedString {
+impl<V: 'static> IntoAnyElement<V> for SharedString {
-    fn into_any(self) -> AnyElement<S> {
+    fn into_any(self) -> AnyElement<V> {
         Text {
             text: self,
             state_type: PhantomData,
@@ -17,7 +17,7 @@ impl<S: 'static + Send + Sync> IntoAnyElement<S> for SharedString {
     }
 }
 
-impl<V: 'static + Send + Sync> IntoAnyElement<V> for &'static str {
+impl<V: 'static> IntoAnyElement<V> for &'static str {
     fn into_any(self) -> AnyElement<V> {
         Text {
             text: self.into(),
@@ -29,8 +29,8 @@ impl<V: 'static + Send + Sync> IntoAnyElement<V> for &'static str {
 
 // TODO: Figure out how to pass `String` to `child` without this.
 // This impl doesn't exist in the `gpui2` crate.
-impl<S: 'static + Send + Sync> IntoAnyElement<S> for String {
+impl<V: 'static> IntoAnyElement<V> for String {
-    fn into_any(self) -> AnyElement<S> {
+    fn into_any(self) -> AnyElement<V> {
         Text {
             text: self.into(),
             state_type: PhantomData,
@@ -44,13 +44,16 @@ pub struct Text<V> {
     state_type: PhantomData<V>,
 }
 
-impl<V: 'static + Send + Sync> IntoAnyElement<V> for Text<V> {
+unsafe impl<V> Send for Text<V> {}
+unsafe impl<V> Sync for Text<V> {}
+
+impl<V: 'static> IntoAnyElement<V> for Text<V> {
     fn into_any(self) -> AnyElement<V> {
         AnyElement::new(self)
     }
 }
 
-impl<V: 'static + Send + Sync> Element for Text<V> {
+impl<V: 'static> Element for Text<V> {
     type ViewState = V;
     type ElementState = Arc<Mutex<Option<TextElementState>>>;
 

crates/gpui2/src/focusable.rs

@@ -135,7 +135,7 @@ pub trait Focusable: Element {
     }
 }
 
-pub trait ElementFocus<V: 'static + Send + Sync>: 'static + Send + Sync {
+pub trait ElementFocus<V: 'static>: 'static + Send + Sync {
     fn as_focusable(&self) -> Option<&FocusEnabled<V>>;
     fn as_focusable_mut(&mut self) -> Option<&mut FocusEnabled<V>>;
 
@@ -200,7 +200,7 @@ pub trait ElementFocus<V: 'static + Send + Sync>: 'static + Send + Sync {
     }
 }
 
-pub struct FocusEnabled<V: 'static + Send + Sync> {
+pub struct FocusEnabled<V> {
     pub focus_handle: Option<FocusHandle>,
     pub focus_listeners: FocusListeners<V>,
     pub focus_style: StyleRefinement,
@@ -208,10 +208,7 @@ pub struct FocusEnabled<V: 'static + Send + Sync> {
     pub in_focus_style: StyleRefinement,
 }
 
-impl<V> FocusEnabled<V>
+impl<V> FocusEnabled<V> {
-where
-    V: 'static + Send + Sync,
-{
     pub fn new() -> Self {
         Self {
             focus_handle: None,
@@ -233,10 +230,7 @@ where
     }
 }
 
-impl<V> ElementFocus<V> for FocusEnabled<V>
+impl<V: 'static> ElementFocus<V> for FocusEnabled<V> {
-where
-    V: 'static + Send + Sync,
-{
     fn as_focusable(&self) -> Option<&FocusEnabled<V>> {
         Some(self)
     }
@@ -246,10 +240,7 @@ where
     }
 }
 
-impl<V> From<FocusHandle> for FocusEnabled<V>
+impl<V> From<FocusHandle> for FocusEnabled<V> {
-where
-    V: 'static + Send + Sync,
-{
     fn from(value: FocusHandle) -> Self {
         Self {
             focus_handle: Some(value),
@@ -263,10 +254,7 @@ where
 
 pub struct FocusDisabled;
 
-impl<V> ElementFocus<V> for FocusDisabled
+impl<V: 'static> ElementFocus<V> for FocusDisabled {
-where
-    V: 'static + Send + Sync,
-{
     fn as_focusable(&self) -> Option<&FocusEnabled<V>> {
         None
     }

crates/gpui2/src/gpui2.rs

@@ -66,15 +66,17 @@ use taffy::TaffyLayoutEngine;
 type AnyBox = Box<dyn Any + Send + Sync>;
 
 pub trait Context {
-    type EntityContext<'a, 'w, T: 'static + Send + Sync>;
+    type EntityContext<'a, 'w, T>;
     type Result<T>;
 
-    fn entity<T: Send + Sync + 'static>(
+    fn entity<T>(
         &mut self,
         build_entity: impl FnOnce(&mut Self::EntityContext<'_, '_, T>) -> T,
-    ) -> Self::Result<Handle<T>>;
+    ) -> Self::Result<Handle<T>>
+    where
+        T: 'static + Send + Sync;
 
-    fn update_entity<T: Send + Sync + 'static, R>(
+    fn update_entity<T: 'static, R>(
         &mut self,
         handle: &Handle<T>,
         update: impl FnOnce(&mut T, &mut Self::EntityContext<'_, '_, T>) -> R,
@@ -105,13 +107,16 @@ impl<T> DerefMut for MainThread<T> {
 }
 
 impl<C: Context> Context for MainThread<C> {
-    type EntityContext<'a, 'w, T: 'static + Send + Sync> = MainThread<C::EntityContext<'a, 'w, T>>;
+    type EntityContext<'a, 'w, T> = MainThread<C::EntityContext<'a, 'w, T>>;
     type Result<T> = C::Result<T>;
 
-    fn entity<T: Send + Sync + 'static>(
+    fn entity<T>(
         &mut self,
         build_entity: impl FnOnce(&mut Self::EntityContext<'_, '_, T>) -> T,
-    ) -> Self::Result<Handle<T>> {
+    ) -> Self::Result<Handle<T>>
+    where
+        T: Any + Send + Sync,
+    {
         self.0.entity(|cx| {
             let cx = unsafe {
                 mem::transmute::<
@@ -123,7 +128,7 @@ impl<C: Context> Context for MainThread<C> {
         })
     }
 
-    fn update_entity<T: Send + Sync + 'static, R>(
+    fn update_entity<T: 'static, R>(
         &mut self,
         handle: &Handle<T>,
         update: impl FnOnce(&mut T, &mut Self::EntityContext<'_, '_, T>) -> R,
@@ -153,13 +158,13 @@ pub trait BorrowAppContext {
         result
     }
 
-    fn set_global<T: Send + Sync + 'static>(&mut self, global: T) {
+    fn set_global<G: Any + Send + Sync>(&mut self, global: G) {
         self.app_mut().set_global(global)
     }
 }
 
-pub trait EventEmitter {
+pub trait EventEmitter: 'static {
-    type Event: Any + Send + Sync + 'static;
+    type Event: Any;
 }
 
 pub trait Flatten<T> {

crates/gpui2/src/interactive.rs

@@ -360,8 +360,9 @@ pub trait StatefulInteractive: StatelessInteractive {
     ) -> Self
     where
         Self: Sized,
-        S: 'static + Send + Sync,
+        S: Any + Send + Sync,
-        R: 'static + Fn(&mut Self::ViewState, &mut ViewContext<Self::ViewState>) -> E + Send + Sync,
+        R: Fn(&mut Self::ViewState, &mut ViewContext<Self::ViewState>) -> E,
+        R: 'static + Send + Sync,
         E: Element<ViewState = Self::ViewState>,
     {
         debug_assert!(
@@ -387,7 +388,7 @@ pub trait StatefulInteractive: StatelessInteractive {
     }
 }
 
-pub trait ElementInteraction<V: 'static + Send + Sync>: 'static + Send + Sync {
+pub trait ElementInteraction<V: 'static>: 'static + Send + Sync {
     fn as_stateless(&self) -> &StatelessInteraction<V>;
     fn as_stateless_mut(&mut self) -> &mut StatelessInteraction<V>;
     fn as_stateful(&self) -> Option<&StatefulInteraction<V>>;
@@ -681,7 +682,7 @@ pub trait ElementInteraction<V: 'static + Send + Sync>: 'static + Send + Sync {
 }
 
 #[derive(Deref, DerefMut)]
-pub struct StatefulInteraction<V: 'static + Send + Sync> {
+pub struct StatefulInteraction<V> {
     pub id: ElementId,
     #[deref]
     #[deref_mut]
@@ -692,10 +693,7 @@ pub struct StatefulInteraction<V: 'static + Send + Sync> {
     drag_listener: Option<DragListener<V>>,
 }
 
-impl<V> ElementInteraction<V> for StatefulInteraction<V>
+impl<V: 'static> ElementInteraction<V> for StatefulInteraction<V> {
-where
-    V: 'static + Send + Sync,
-{
     fn as_stateful(&self) -> Option<&StatefulInteraction<V>> {
         Some(self)
     }
@@ -713,10 +711,7 @@ where
     }
 }
 
-impl<V> From<ElementId> for StatefulInteraction<V>
+impl<V> From<ElementId> for StatefulInteraction<V> {
-where
-    V: 'static + Send + Sync,
-{
     fn from(id: ElementId) -> Self {
         Self {
             id,
@@ -729,7 +724,7 @@ where
     }
 }
 
-type DropListener<V> = dyn Fn(&mut V, AnyBox, &mut ViewContext<V>) + Send + Sync;
+type DropListener<V> = dyn Fn(&mut V, AnyBox, &mut ViewContext<V>) + 'static + Send + Sync;
 
 pub struct StatelessInteraction<V> {
     pub dispatch_context: DispatchContext,
@@ -745,10 +740,7 @@ pub struct StatelessInteraction<V> {
     drop_listeners: SmallVec<[(TypeId, Arc<DropListener<V>>); 2]>,
 }
 
-impl<V> StatelessInteraction<V>
+impl<V> StatelessInteraction<V> {
-where
-    V: 'static + Send + Sync,
-{
     pub fn into_stateful(self, id: impl Into<ElementId>) -> StatefulInteraction<V> {
         StatefulInteraction {
             id: id.into(),
@@ -840,10 +832,7 @@ impl<V> Default for StatelessInteraction<V> {
     }
 }
 
-impl<V> ElementInteraction<V> for StatelessInteraction<V>
+impl<V: 'static> ElementInteraction<V> for StatelessInteraction<V> {
-where
-    V: 'static + Send + Sync,
-{
     fn as_stateful(&self) -> Option<&StatefulInteraction<V>> {
         None
     }
@@ -918,9 +907,7 @@ pub struct ClickEvent {
 
 pub struct Drag<S, R, V, E>
 where
-    S: 'static + Send + Sync,
     R: Fn(&mut V, &mut ViewContext<V>) -> E,
-    V: 'static + Send + Sync,
     E: Element<ViewState = V>,
 {
     pub state: S,
@@ -930,9 +917,7 @@ where
 
 impl<S, R, V, E> Drag<S, R, V, E>
 where
-    S: 'static + Send + Sync,
+    R: Fn(&mut V, &mut ViewContext<V>) -> E,
-    R: Fn(&mut V, &mut ViewContext<V>) -> E + Send + Sync,
-    V: 'static + Send + Sync,
     E: Element<ViewState = V>,
 {
     pub fn new(state: S, render_drag_handle: R) -> Self {

crates/gpui2/src/platform.rs

@@ -102,7 +102,7 @@ pub(crate) trait Platform: 'static {
     fn delete_credentials(&self, url: &str) -> Result<()>;
 }
 
-pub trait PlatformDisplay: Debug {
+pub trait PlatformDisplay: Send + Sync + Debug {
     fn id(&self) -> DisplayId;
     fn as_any(&self) -> &dyn Any;
     fn bounds(&self) -> Bounds<GlobalPixels>;

crates/gpui2/src/subscription.rs

@@ -21,7 +21,7 @@ struct SubscriberSetState<EmitterKey, Callback> {
 
 impl<EmitterKey, Callback> SubscriberSet<EmitterKey, Callback>
 where
-    EmitterKey: 'static + Send + Sync + Ord + Clone + Debug,
+    EmitterKey: 'static + Ord + Clone + Debug,
     Callback: 'static + Send + Sync,
 {
     pub fn new() -> Self {
@@ -96,7 +96,7 @@ where
 
 #[must_use]
 pub struct Subscription {
-    unsubscribe: Option<Box<dyn FnOnce() + Send + Sync>>,
+    unsubscribe: Option<Box<dyn FnOnce()>>,
 }
 
 impl Subscription {

crates/gpui2/src/view.rs

@@ -6,12 +6,12 @@ use crate::{
 };
 use std::{marker::PhantomData, sync::Arc};
 
-pub struct View<V: Send + Sync> {
+pub struct View<V> {
     state: Handle<V>,
     render: Arc<dyn Fn(&mut V, &mut ViewContext<V>) -> AnyElement<V> + Send + Sync + 'static>,
 }
 
-impl<V: 'static + Send + Sync> View<V> {
+impl<V: 'static> View<V> {
     pub fn into_any(self) -> AnyView {
         AnyView {
             view: Arc::new(Mutex::new(self)),
@@ -19,7 +19,7 @@ impl<V: 'static + Send + Sync> View<V> {
     }
 }
 
-impl<V: Send + Sync> Clone for View<V> {
+impl<V> Clone for View<V> {
     fn clone(&self) -> Self {
         Self {
             state: self.state.clone(),
@@ -34,7 +34,6 @@ pub fn view<V, E>(
 ) -> View<V>
 where
     E: IntoAnyElement<V>,
-    V: 'static + Send + Sync,
 {
     View {
         state,
@@ -42,9 +41,7 @@ where
     }
 }
 
-impl<V: 'static + Send + Sync, ParentViewState: 'static + Send + Sync>
+impl<V: 'static, ParentViewState: 'static> IntoAnyElement<ParentViewState> for View<V> {
-    IntoAnyElement<ParentViewState> for View<V>
-{
     fn into_any(self) -> AnyElement<ParentViewState> {
         AnyElement::new(EraseViewState {
             view: self,
@@ -53,7 +50,7 @@ impl<V: 'static + Send + Sync, ParentViewState: 'static + Send + Sync>
     }
 }
 
-impl<V: 'static + Send + Sync> Element for View<V> {
+impl<V: 'static> Element for View<V> {
     type ViewState = ();
     type ElementState = AnyElement<V>;
 
@@ -94,26 +91,21 @@ impl<V: 'static + Send + Sync> Element for View<V> {
     }
 }
 
-struct EraseViewState<V: 'static + Send + Sync, ParentV> {
+struct EraseViewState<V, ParentV> {
     view: View<V>,
     parent_view_state_type: PhantomData<ParentV>,
 }
 
-impl<V, ParentV> IntoAnyElement<ParentV> for EraseViewState<V, ParentV>
+unsafe impl<V, ParentV> Send for EraseViewState<V, ParentV> {}
-where
+unsafe impl<V, ParentV> Sync for EraseViewState<V, ParentV> {}
-    V: 'static + Send + Sync,
+
-    ParentV: 'static + Send + Sync,
+impl<V: 'static, ParentV: 'static> IntoAnyElement<ParentV> for EraseViewState<V, ParentV> {
-{
     fn into_any(self) -> AnyElement<ParentV> {
         AnyElement::new(self)
     }
 }
 
-impl<V, ParentV> Element for EraseViewState<V, ParentV>
+impl<V: 'static, ParentV: 'static> Element for EraseViewState<V, ParentV> {
-where
-    V: 'static + Send + Sync,
-    ParentV: 'static + Send + Sync,
-{
     type ViewState = ParentV;
     type ElementState = AnyBox;
 
@@ -150,14 +142,14 @@ where
     }
 }
 
-trait ViewObject: 'static + Send + Sync {
+trait ViewObject: Send + Sync {
     fn entity_id(&self) -> EntityId;
     fn initialize(&mut self, cx: &mut WindowContext) -> AnyBox;
     fn layout(&mut self, element: &mut AnyBox, cx: &mut WindowContext) -> LayoutId;
     fn paint(&mut self, bounds: Bounds<Pixels>, element: &mut AnyBox, cx: &mut WindowContext);
 }
 
-impl<V: Send + Sync + 'static> ViewObject for View<V> {
+impl<V: 'static> ViewObject for View<V> {
     fn entity_id(&self) -> EntityId {
         self.state.entity_id
     }
@@ -195,10 +187,7 @@ pub struct AnyView {
     view: Arc<Mutex<dyn ViewObject>>,
 }
 
-impl<ParentV> IntoAnyElement<ParentV> for AnyView
+impl<ParentV: 'static> IntoAnyElement<ParentV> for AnyView {
-where
-    ParentV: 'static + Send + Sync,
-{
     fn into_any(self) -> AnyElement<ParentV> {
         AnyElement::new(EraseAnyViewState {
             view: self,
@@ -249,19 +238,16 @@ struct EraseAnyViewState<ParentViewState> {
     parent_view_state_type: PhantomData<ParentViewState>,
 }
 
-impl<ParentV> IntoAnyElement<ParentV> for EraseAnyViewState<ParentV>
+unsafe impl<ParentV> Send for EraseAnyViewState<ParentV> {}
-where
+unsafe impl<ParentV> Sync for EraseAnyViewState<ParentV> {}
-    ParentV: 'static + Send + Sync,
+
-{
+impl<ParentV: 'static> IntoAnyElement<ParentV> for EraseAnyViewState<ParentV> {
     fn into_any(self) -> AnyElement<ParentV> {
         AnyElement::new(self)
     }
 }
 
-impl<ParentV> Element for EraseAnyViewState<ParentV>
+impl<ParentV: 'static> Element for EraseAnyViewState<ParentV> {
-where
-    ParentV: 'static + Send + Sync,
-{
     type ViewState = ParentV;
     type ElementState = AnyBox;
 

crates/gpui2/src/window.rs

@@ -428,11 +428,11 @@ impl<'a, 'w> WindowContext<'a, 'w> {
 
     pub fn update_global<G, R>(&mut self, f: impl FnOnce(&mut G, &mut Self) -> R) -> R
     where
-        G: 'static + Send + Sync,
+        G: 'static,
     {
         let mut global = self.app.lease_global::<G>();
-        let result = f(global.as_mut(), self);
+        let result = f(&mut global, self);
-        self.app.set_global(global);
+        self.app.end_global_lease(global);
         result
     }
 
@@ -1129,23 +1129,26 @@ impl<'a, 'w> MainThread<WindowContext<'a, 'w>> {
 }
 
 impl Context for WindowContext<'_, '_> {
-    type EntityContext<'a, 'w, T: 'static + Send + Sync> = ViewContext<'a, 'w, T>;
+    type EntityContext<'a, 'w, T> = ViewContext<'a, 'w, T>;
     type Result<T> = T;
 
-    fn entity<T: Send + Sync + 'static>(
+    fn entity<T>(
         &mut self,
         build_entity: impl FnOnce(&mut Self::EntityContext<'_, '_, T>) -> T,
-    ) -> Handle<T> {
+    ) -> Handle<T>
+    where
+        T: Any + Send + Sync,
+    {
         let slot = self.app.entities.reserve();
         let entity = build_entity(&mut ViewContext::mutable(
             &mut *self.app,
             &mut self.window,
-            slot.entity_id,
+            slot.downgrade(),
         ));
         self.entities.insert(slot, entity)
     }
 
-    fn update_entity<T: Send + Sync + 'static, R>(
+    fn update_entity<T: 'static, R>(
         &mut self,
         handle: &Handle<T>,
         update: impl FnOnce(&mut T, &mut Self::EntityContext<'_, '_, T>) -> R,
@@ -1153,7 +1156,7 @@ impl Context for WindowContext<'_, '_> {
         let mut entity = self.entities.lease(handle);
         let result = update(
             &mut *entity,
-            &mut ViewContext::mutable(&mut *self.app, &mut *self.window, handle.entity_id),
+            &mut ViewContext::mutable(&mut *self.app, &mut *self.window, handle.downgrade()),
         );
         self.entities.end_lease(entity);
         result
@@ -1245,11 +1248,14 @@ pub trait BorrowWindow: BorrowAppContext {
             .unwrap_or_default()
     }
 
-    fn with_element_state<S: 'static + Send + Sync, R>(
+    fn with_element_state<S, R>(
         &mut self,
         id: ElementId,
         f: impl FnOnce(Option<S>, &mut Self) -> (R, S),
-    ) -> R {
+    ) -> R
+    where
+        S: Any + Send + Sync,
+    {
         self.with_element_id(id, |global_id, cx| {
             if let Some(any) = cx
                 .window_mut()
@@ -1278,11 +1284,14 @@ pub trait BorrowWindow: BorrowAppContext {
         })
     }
 
-    fn with_optional_element_state<S: 'static + Send + Sync, R>(
+    fn with_optional_element_state<S, R>(
         &mut self,
         element_id: Option<ElementId>,
         f: impl FnOnce(Option<S>, &mut Self) -> (R, S),
-    ) -> R {
+    ) -> R
+    where
+        S: Any + Send + Sync,
+    {
         if let Some(element_id) = element_id {
             self.with_element_state(element_id, f)
         } else {
@@ -1318,13 +1327,12 @@ impl BorrowWindow for WindowContext<'_, '_> {
     }
 }
 
-pub struct ViewContext<'a, 'w, S> {
+pub struct ViewContext<'a, 'w, V> {
     window_cx: WindowContext<'a, 'w>,
-    entity_type: PhantomData<S>,
+    view_state: WeakHandle<V>,
-    entity_id: EntityId,
 }
 
-impl<S> BorrowAppContext for ViewContext<'_, '_, S> {
+impl<V> BorrowAppContext for ViewContext<'_, '_, V> {
     fn app_mut(&mut self) -> &mut AppContext {
         &mut *self.window_cx.app
     }
@@ -1340,17 +1348,16 @@ impl<S> BorrowWindow for ViewContext<'_, '_, S> {
     }
 }
 
-impl<'a, 'w, V: Send + Sync + 'static> ViewContext<'a, 'w, V> {
+impl<'a, 'w, V: 'static> ViewContext<'a, 'w, V> {
-    fn mutable(app: &'a mut AppContext, window: &'w mut Window, entity_id: EntityId) -> Self {
+    fn mutable(app: &'a mut AppContext, window: &'w mut Window, view_state: WeakHandle<V>) -> Self {
         Self {
             window_cx: WindowContext::mutable(app, window),
-            entity_id,
+            view_state,
-            entity_type: PhantomData,
         }
     }
 
     pub fn handle(&self) -> WeakHandle<V> {
-        self.entities.weak_handle(self.entity_id)
+        self.view_state.clone()
     }
 
     pub fn stack<R>(&mut self, order: u32, f: impl FnOnce(&mut Self) -> R) -> R {
@@ -1360,18 +1367,25 @@ impl<'a, 'w, V: Send + Sync + 'static> ViewContext<'a, 'w, V> {
         result
     }
 
-    pub fn on_next_frame(&mut self, f: impl FnOnce(&mut V, &mut ViewContext<V>) + Send + 'static) {
+    pub fn on_next_frame(&mut self, f: impl FnOnce(&mut V, &mut ViewContext<V>) + Send + 'static)
+    where
+        V: Any + Send + Sync,
+    {
         let entity = self.handle();
         self.window_cx.on_next_frame(move |cx| {
             entity.update(cx, f).ok();
         });
     }
 
-    pub fn observe<E: Send + Sync + 'static>(
+    pub fn observe<E>(
         &mut self,
         handle: &Handle<E>,
         on_notify: impl Fn(&mut V, Handle<E>, &mut ViewContext<'_, '_, V>) + Send + Sync + 'static,
-    ) -> Subscription {
+    ) -> Subscription
+    where
+        E: 'static,
+        V: Any + Send + Sync,
+    {
         let this = self.handle();
         let handle = handle.downgrade();
         let window_handle = self.window.handle;
@@ -1391,7 +1405,7 @@ impl<'a, 'w, V: Send + Sync + 'static> ViewContext<'a, 'w, V> {
         )
     }
 
-    pub fn subscribe<E: EventEmitter + Send + Sync + 'static>(
+    pub fn subscribe<E: EventEmitter>(
         &mut self,
         handle: &Handle<E>,
         on_event: impl Fn(&mut V, Handle<E>, &E::Event, &mut ViewContext<'_, '_, V>)
@@ -1425,7 +1439,7 @@ impl<'a, 'w, V: Send + Sync + 'static> ViewContext<'a, 'w, V> {
     ) -> Subscription {
         let window_handle = self.window.handle;
         self.app.release_listeners.insert(
-            self.entity_id,
+            self.view_state.entity_id,
             Box::new(move |this, cx| {
                 let this = this.downcast_mut().expect("invalid entity type");
                 // todo!("are we okay with silently swallowing the error?")
@@ -1434,11 +1448,14 @@ impl<'a, 'w, V: Send + Sync + 'static> ViewContext<'a, 'w, V> {
         )
     }
 
-    pub fn observe_release<E: Send + Sync + 'static>(
+    pub fn observe_release<T: 'static>(
         &mut self,
-        handle: &Handle<E>,
+        handle: &Handle<T>,
-        on_release: impl Fn(&mut V, &mut E, &mut ViewContext<'_, '_, V>) + Send + Sync + 'static,
+        on_release: impl Fn(&mut V, &mut T, &mut ViewContext<'_, '_, V>) + Send + Sync + 'static,
-    ) -> Subscription {
+    ) -> Subscription
+    where
+        V: Any + Send + Sync,
+    {
         let this = self.handle();
         let window_handle = self.window.handle;
         self.app.release_listeners.insert(
@@ -1456,7 +1473,7 @@ impl<'a, 'w, V: Send + Sync + 'static> ViewContext<'a, 'w, V> {
     pub fn notify(&mut self) {
         self.window_cx.notify();
         self.window_cx.app.push_effect(Effect::Notify {
-            emitter: self.entity_id,
+            emitter: self.view_state.entity_id,
         });
     }
 
@@ -1595,8 +1612,8 @@ impl<'a, 'w, V: Send + Sync + 'static> ViewContext<'a, 'w, V> {
         G: 'static + Send + Sync,
     {
         let mut global = self.app.lease_global::<G>();
-        let result = f(global.as_mut(), self);
+        let result = f(&mut global, self);
-        self.app.restore_global(global);
+        self.app.end_global_lease(global);
         result
     }
 
@@ -1630,9 +1647,13 @@ impl<'a, 'w, V: Send + Sync + 'static> ViewContext<'a, 'w, V> {
     }
 }
 
-impl<'a, 'w, V: EventEmitter + Send + Sync + 'static> ViewContext<'a, 'w, V> {
+impl<'a, 'w, V> ViewContext<'a, 'w, V>
+where
+    V: EventEmitter,
+    V::Event: Any + Send + Sync,
+{
     pub fn emit(&mut self, event: V::Event) {
-        let emitter = self.entity_id;
+        let emitter = self.view_state.entity_id;
         self.app.push_effect(Effect::Emit {
             emitter,
             event: Box::new(event),
@@ -1640,30 +1661,30 @@ impl<'a, 'w, V: EventEmitter + Send + Sync + 'static> ViewContext<'a, 'w, V> {
     }
 }
 
-impl<'a, 'w, V> Context for ViewContext<'a, 'w, V>
+impl<'a, 'w, V> Context for ViewContext<'a, 'w, V> {
-where
+    type EntityContext<'b, 'c, U> = ViewContext<'b, 'c, U>;
-    V: 'static + Send + Sync,
-{
-    type EntityContext<'b, 'c, U: 'static + Send + Sync> = ViewContext<'b, 'c, U>;
     type Result<U> = U;
 
-    fn entity<T2: Send + Sync + 'static>(
+    fn entity<T>(
         &mut self,
-        build_entity: impl FnOnce(&mut Self::EntityContext<'_, '_, T2>) -> T2,
+        build_entity: impl FnOnce(&mut Self::EntityContext<'_, '_, T>) -> T,
-    ) -> Handle<T2> {
+    ) -> Handle<T>
+    where
+        T: 'static + Send + Sync,
+    {
         self.window_cx.entity(build_entity)
     }
 
-    fn update_entity<U: 'static + Send + Sync, R>(
+    fn update_entity<T: 'static, R>(
         &mut self,
-        handle: &Handle<U>,
+        handle: &Handle<T>,
-        update: impl FnOnce(&mut U, &mut Self::EntityContext<'_, '_, U>) -> R,
+        update: impl FnOnce(&mut T, &mut Self::EntityContext<'_, '_, T>) -> R,
     ) -> R {
         self.window_cx.update_entity(handle, update)
     }
 }
 
-impl<'a, 'w, S: 'static> std::ops::Deref for ViewContext<'a, 'w, S> {
+impl<'a, 'w, V> std::ops::Deref for ViewContext<'a, 'w, V> {
     type Target = WindowContext<'a, 'w>;
 
     fn deref(&self) -> &Self::Target {
@@ -1671,7 +1692,7 @@ impl<'a, 'w, S: 'static> std::ops::Deref for ViewContext<'a, 'w, S> {
     }
 }
 
-impl<'a, 'w, S: 'static> std::ops::DerefMut for ViewContext<'a, 'w, S> {
+impl<'a, 'w, V> std::ops::DerefMut for ViewContext<'a, 'w, V> {
     fn deref_mut(&mut self) -> &mut Self::Target {
         &mut self.window_cx
     }
@@ -1687,9 +1708,9 @@ impl WindowId {
 }
 
 #[derive(PartialEq, Eq)]
-pub struct WindowHandle<S> {
+pub struct WindowHandle<V> {
     id: WindowId,
-    state_type: PhantomData<S>,
+    state_type: PhantomData<V>,
 }
 
 impl<S> Copy for WindowHandle<S> {}