Adds an example of using the new columnar API to clone world.

examples/columnar_clone.rs

@@ -0,0 +1,142 @@
+use core::any::TypeId;
+use std::ops::{Deref, DerefMut};
+
+use hecs::{Archetype, ColumnBatchBuilder, ColumnBatchType, Component, World};
+
+fn main() {
+    let mut world = CloneableWorld {
+        inner: World::new(),
+        clone_registry: CloneRegistry::default()
+            .register::<String>()
+            .register::<u32>(),
+    };
+
+    world.spawn((4u32,));
+    world.spawn((8u32, "test".to_string()));
+    world.spawn(("test".to_string(),));
+
+    let cloned = world.clone();
+
+    assert_eq!(
+        world.query::<&u32>().iter().count(),
+        cloned.query::<&u32>().iter().count()
+    );
+    assert_eq!(
+        world.query::<&String>().iter().count(),
+        cloned.query::<&String>().iter().count()
+    );
+
+    for (left, right) in world
+        .query::<&u32>()
+        .iter()
+        .zip(cloned.query::<&u32>().iter())
+    {
+        assert_eq!(left, right);
+    }
+
+    for (left, right) in world
+        .query::<&String>()
+        .iter()
+        .zip(cloned.query::<&String>().iter())
+    {
+        assert_eq!(left, right);
+    }
+}
+
+/// An opaque registry that holds data that helps a World clone itself.
+#[derive(Clone, Default)]
+struct CloneRegistry(Vec<CloneEntry>);
+
+impl CloneRegistry {
+    /// Registers `T` with the registry, enabling `T` to be cloned in any
+    /// archetypes that contain it.
+    pub fn register<T: Clone + Component>(mut self) -> Self {
+        if !self.0.iter().any(|item| item.type_id == TypeId::of::<T>()) {
+            self.0.push(register::<T>());
+        }
+        self
+    }
+}
+
+#[derive(Clone)]
+struct CloneEntry {
+    type_id: TypeId,
+    add_type: fn(&mut ColumnBatchType) -> (),
+    add_values: fn(&mut ColumnBatchBuilder, &Archetype) -> (),
+}
+fn register<T: Component + Clone>() -> CloneEntry {
+    CloneEntry {
+        type_id: TypeId::of::<T>(),
+        add_type: |batch_type| {
+            batch_type.add::<T>();
+        },
+        add_values: |batch, arch| {
+            let mut writer = batch.writer::<T>().unwrap();
+            for item in arch.get::<T>().unwrap().iter() {
+                if writer.push(item.clone()).is_err() {
+                    panic!()
+                }
+            }
+        },
+    }
+}
+
+pub struct CloneableWorld {
+    inner: World,
+    clone_registry: CloneRegistry,
+}
+
+impl Deref for CloneableWorld {
+    type Target = World;
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+impl DerefMut for CloneableWorld {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.inner
+    }
+}
+
+impl Clone for CloneableWorld {
+    fn clone(&self) -> Self {
+        let mut new_world = Self {
+            inner: World::new(),
+            clone_registry: self.clone_registry.clone(),
+        };
+
+        for archetype in self.archetypes() {
+            debug_assert!(archetype.component_types().all(|item| self
+                .clone_registry
+                .0
+                .iter()
+                .any(|register| register.type_id == item)));
+            let mut types = ColumnBatchType::new();
+            for entry in self
+                .clone_registry
+                .0
+                .iter()
+                .filter(|item| archetype.has_dynamic(item.type_id))
+            {
+                (entry.add_type)(&mut types);
+            }
+            let mut batch = types.into_batch(archetype.len());
+            for entry in self
+                .clone_registry
+                .0
+                .iter()
+                .filter(|item| archetype.has_dynamic(item.type_id))
+            {
+                (entry.add_values)(&mut batch, archetype);
+            }
+            let entities: Box<[_]> = archetype
+                .ids()
+                .iter()
+                .map(|id| unsafe { self.find_entity_from_id(*id) })
+                .collect();
+            new_world.spawn_column_batch_at(&entities, batch.build().unwrap());
+        }
+
+        new_world
+    }
+}