Add World::iter_resources() and World::iter_resources_mut() methods

crates/bevy_ecs/src/world/mod.rs

@@ -2184,6 +2184,194 @@ impl World {
                 .get_mut_by_id(component_id)
         }
     }
+
+    /// Iterates over all resources in the world
+    ///
+    /// # Examples
+    ///
+    /// ## Printing the size of all resources
+    ///
+    /// ```
+    /// # use bevy_ecs::prelude::*;
+    /// # #[derive(Resource)]
+    /// # struct A(u32);
+    /// # #[derive(Resource)]
+    /// # struct B(u32);
+    /// #
+    /// # let mut world = World::new();
+    /// # world.insert_resource(A(1));
+    /// # world.insert_resource(B(2));
+    /// let mut total = 0;
+    /// for (info, _) in world.iter_resources() {
+    ///    println!("Resource: {}", info.name());
+    ///    println!("Size: {} bytes", info.layout().size());
+    ///    total += info.layout().size();
+    /// }
+    /// println!("----------------");
+    /// println!("Total size: {} bytes", total);
+    /// # assert_eq!(total, std::mem::size_of::<A>() + std::mem::size_of::<B>());
+    /// ```
+    ///
+    /// ## Dynamically running closures for resources matching specific `TypeId`s
+    ///
+    /// ```
+    /// # use bevy_ecs::prelude::*;
+    /// # use std::collections::HashMap;
+    /// # use std::any::TypeId;
+    /// # use bevy_ptr::Ptr;
+    /// # #[derive(Resource)]
+    /// # struct A(u32);
+    /// # #[derive(Resource)]
+    /// # struct B(u32);
+    /// #
+    /// # let mut world = World::new();
+    /// # world.insert_resource(A(1));
+    /// # world.insert_resource(B(2));
+    /// #
+    /// // In this example, `A` and `B` are resources. We deliberately do not use the
+    /// // `bevy_reflect` crate here to showcase the low-level `Ptr` usage. You should
+    /// // probably use something like `ReflectFromPtr` in a real-world scenario.
+    ///
+    /// // Create the hash map that will store the closures for each resource type
+    /// let mut closures: HashMap<TypeId, Box<dyn Fn(&Ptr<'_>)>> = HashMap::new();
+    ///
+    /// // Add closure for `A`
+    /// closures.insert(TypeId::of::<A>(), Box::new(|ptr| {
+    ///     let a = unsafe { &ptr.deref::<A>() };
+    /// #   assert_eq!(a.0, 1);
+    ///     // ... do something with `a` here
+    /// }));
+    ///
+    /// // Add closure for `B`
+    /// closures.insert(TypeId::of::<B>(), Box::new(|ptr| {
+    ///     let b = unsafe { &ptr.deref::<B>() };
+    /// #   assert_eq!(b.0, 2);
+    ///     // ... do something with `b` here
+    /// }));
+    ///
+    /// // Iterate all resources, in order to run the closures for each matching resource type
+    /// for (info, ptr) in world.iter_resources() {
+    ///     let Some(type_id) = info.type_id() else {
+    ///        // It's possible for resources to not have a `TypeId` (e.g. non-Rust resources
+    ///        // dynamically inserted via a scripting language) in which case we can't match them.
+    ///        continue;
+    ///     };
+    ///
+    ///     let Some(closure) = closures.get(&type_id) else {
+    ///        // No closure for this resource type, skip it.
+    ///        continue;
+    ///     };
+    ///
+    ///     // Run the closure for the resource
+    ///     closure(&ptr);
+    /// }
+    /// ```
+    pub fn iter_resources(&self) -> impl Iterator<Item = (&ComponentInfo, Ptr<'_>)> {
+        self.storages.resources.iter().map(|(component_id, data)| {
+            let component_info = self.components.get_info(component_id).unwrap_or_else(|| {
+                panic!("ComponentInfo should exist for all resources in the world, but it does not for {:?}", component_id);
+            });
+            let ptr = data.get_data().unwrap_or_else(|| {
+                panic!(
+                    "When iterating all resources, resource of type {} was supposed to exist, but did not.",
+                    component_info.name()
+                )
+            });
+            (component_info, ptr)
+        })
+    }
+
+    /// Mutably iterates over all resources in the world
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use bevy_ecs::prelude::*;
+    /// # use bevy_ecs::change_detection::MutUntyped;
+    /// # use std::collections::HashMap;
+    /// # use std::any::TypeId;
+    /// # #[derive(Resource)]
+    /// # struct A(u32);
+    /// # #[derive(Resource)]
+    /// # struct B(u32);
+    /// #
+    /// # let mut world = World::new();
+    /// # world.insert_resource(A(1));
+    /// # world.insert_resource(B(2));
+    /// #
+    /// // In this example, `A` and `B` are resources. We deliberately do not use the
+    /// // `bevy_reflect` crate here to showcase the low-level `MutUntyped` usage. You should
+    /// // probably use something like `ReflectFromPtr` in a real-world scenario.
+    ///
+    /// // Create the hash map that will store the mutator closures for each resource type
+    /// let mut mutators: HashMap<TypeId, Box<dyn Fn(&mut MutUntyped<'_>)>> = HashMap::new();
+    ///
+    /// // Add mutator closure for `A`
+    /// mutators.insert(TypeId::of::<A>(), Box::new(|mut_untyped| {
+    ///     // Note: `MutUntyped::as_mut()` automatically marks the resource as changed
+    ///     // for ECS change detection, and gives us a `PtrMut` we can use to mutate the resource.
+    ///     let a = unsafe { &mut mut_untyped.as_mut().deref_mut::<A>() };
+    /// #   a.0 += 1;
+    ///     // ... mutate `a` here
+    /// }));
+    ///
+    /// // Add mutator closure for `B`
+    /// mutators.insert(TypeId::of::<B>(), Box::new(|mut_untyped| {
+    ///     let b = unsafe { &mut mut_untyped.as_mut().deref_mut::<B>() };
+    /// #   b.0 += 1;
+    ///     // ... mutate `b` here
+    /// }));
+    ///
+    /// // Iterate all resources, in order to run the mutator closures for each matching resource type
+    /// for (info, mut mut_untyped) in world.iter_resources_mut() {
+    ///     let Some(type_id) = info.type_id() else {
+    ///        // It's possible for resources to not have a `TypeId` (e.g. non-Rust resources
+    ///        // dynamically inserted via a scripting language) in which case we can't match them.
+    ///        continue;
+    ///     };
+    ///
+    ///     let Some(mutator) = mutators.get(&type_id) else {
+    ///        // No mutator closure for this resource type, skip it.
+    ///        continue;
+    ///     };
+    ///
+    ///     // Run the mutator closure for the resource
+    ///     mutator(&mut mut_untyped);
+    /// }
+    /// # assert_eq!(world.resource::<A>().0, 2);
+    /// # assert_eq!(world.resource::<B>().0, 3);
+    /// ```
+    pub fn iter_resources_mut(&mut self) -> impl Iterator<Item = (&ComponentInfo, MutUntyped<'_>)> {
+        self.storages.resources.iter().map(|(component_id, data)| {
+            let component_info = self.components.get_info(component_id).unwrap_or_else(|| {
+                panic!("ComponentInfo should exist for all resources in the world, but it does not for {:?}", component_id);
+            });
+
+            let (ptr, ticks) = data.get_with_ticks().unwrap_or_else(|| {
+                panic!(
+                    "When iterating all resources, resource of type {} was supposed to exist, but did not.",
+                    component_info.name()
+                )
+            });
+
+            // SAFETY:
+            // - We have exclusive access to the world, so no other code can be aliasing the `TickCells`
+            // - We only hold one `TicksMut` at a time, and we let go of it before getting the next one
+            let ticks = unsafe {
+                TicksMut::from_tick_cells(ticks, self.last_change_tick(), self.read_change_tick())
+            };
+
+            let mut_untyped = MutUntyped {
+                // SAFETY:
+                // - We have exclusive access to the world, so no other code can be aliasing the `Ptr`
+                // - We iterate one resource at a time, and we let go of each `PtrMut` before getting the next one
+                value: unsafe { ptr.assert_unique() },
+                ticks,
+            };
+
+            (component_info, mut_untyped)
+        })
+    }
 }
 
 // Schedule-related methods
@@ -2495,6 +2683,9 @@ mod tests {
     #[derive(Resource)]
     struct TestResource(u32);
 
+    #[derive(Resource)]
+    struct TestResource2(String);
+
     #[test]
     fn get_resource_by_id() {
         let mut world = World::new();
@@ -2796,4 +2987,63 @@ mod tests {
         let mut world = World::new();
         world.spawn(());
     }
+
+    #[test]
+    fn iterate_resources() {
+        let mut world = World::new();
+
+        world.insert_resource(TestResource(42));
+        world.insert_resource(TestResource2("Hello, world!".to_string()));
+
+        let mut iter = world.iter_resources();
+
+        let (info, ptr) = iter.next().unwrap();
+        assert_eq!(info.name(), std::any::type_name::<TestResource>());
+        // SAFETY: We know that the resource is of type `TestResource`
+        assert_eq!(unsafe { ptr.deref::<TestResource>().0 }, 42);
+
+        let (info, ptr) = iter.next().unwrap();
+        assert_eq!(info.name(), std::any::type_name::<TestResource2>());
+        assert_eq!(
+            // SAFETY: We know that the resource is of type `TestResource2`
+            unsafe { &ptr.deref::<TestResource2>().0 },
+            &"Hello, world!".to_string()
+        );
+
+        assert!(iter.next().is_none());
+    }
+
+    #[test]
+    fn iterate_resources_mut() {
+        let mut world = World::new();
+
+        world.insert_resource(TestResource(42));
+        world.insert_resource(TestResource2("Hello, world!".to_string()));
+
+        let mut iter = world.iter_resources_mut();
+
+        let (info, mut mut_untyped) = iter.next().unwrap();
+        assert_eq!(info.name(), std::any::type_name::<TestResource>());
+        // SAFETY: We know that the resource is of type `TestResource`
+        unsafe {
+            mut_untyped.as_mut().deref_mut::<TestResource>().0 = 43;
+        }
+
+        let (info, mut mut_untyped) = iter.next().unwrap();
+        assert_eq!(info.name(), std::any::type_name::<TestResource2>());
+        // SAFETY: We know that the resource is of type `TestResource2`
+        unsafe {
+            mut_untyped.as_mut().deref_mut::<TestResource2>().0 = "Hello, world?".to_string();
+        }
+
+        assert!(iter.next().is_none());
+
+        std::mem::drop(iter);
+
+        assert_eq!(world.resource::<TestResource>().0, 43);
+        assert_eq!(
+            world.resource::<TestResource2>().0,
+            "Hello, world?".to_string()
+        );
+    }
 }