feat(ecs): add creating static entities

3 files changed, 52 insertions, 5 deletions

diff --git a/ecs/src/entity.rs b/ecs/src/entity.rs
index abc5991..18f229a 100644
--- a/ecs/src/entity.rs
+++ b/ecs/src/entity.rs
@@ -1,5 +1,9 @@
 use std::sync::atomic::{AtomicU64, Ordering};
 
+use linkme::distributed_slice;
+
+use crate::World;
+
 static NEXT_UID: AtomicU64 = AtomicU64::new(0);
 
 /// Unique entity ID.
@@ -28,3 +32,29 @@ impl Uid
         }
     }
 }
+
+#[macro_export]
+macro_rules! static_entity {
+    ($visibility: vis $ident: ident, $components: expr) => {
+        $visibility static $ident: ::std::sync::LazyLock<$crate::entity::Uid> =
+            ::std::sync::LazyLock::new(|| $crate::entity::Uid::new_unique());
+
+        $crate::private::paste::paste! {
+            mod [<__ecs_ $ident:lower _static_entity_priv>] {
+                use super::*;
+
+                #[$crate::private::linkme::distributed_slice(
+                    $crate::entity::CREATE_STATIC_ENTITIES
+                )]
+                #[linkme(crate=$crate::private::linkme)]
+                static CREATE_STATIC_ENTITY: fn(&$crate::World) = |world| {
+                    world.create_entity_with_uid($components, *$ident);
+                };
+            }
+        }
+    }
+}
+
+#[distributed_slice]
+#[doc(hidden)]
+pub static CREATE_STATIC_ENTITIES: [fn(&World)];
diff --git a/ecs/src/lib.rs b/ecs/src/lib.rs
index 3c517dd..6725d81 100644
--- a/ecs/src/lib.rs
+++ b/ecs/src/lib.rs
@@ -11,7 +11,7 @@ use std::sync::Arc;
 use crate::actions::Action;
 use crate::component::storage::Storage as ComponentStorage;
 use crate::component::{Component, Id as ComponentId, Sequence as ComponentSequence};
-use crate::entity::Uid as EntityUid;
+use crate::entity::{Uid as EntityUid, CREATE_STATIC_ENTITIES};
 use crate::event::component::{
     create_added_id as create_component_added_event_id,
     create_removed_id as create_component_removed_event_id,
@@ -42,6 +42,9 @@ pub mod system;
 pub mod tuple;
 pub mod type_name;
 
+#[doc(hidden)]
+pub mod private;
+
 mod archetype;
 mod util;
 
@@ -75,7 +78,6 @@ impl World
     ///
     /// # Panics
     /// Will panic if mutable internal lock cannot be acquired.
-    #[cfg_attr(feature = "debug", tracing::instrument(skip_all))]
     pub fn create_entity<Comps>(&mut self, components: Comps) -> EntityUid
     where
         Comps: ComponentSequence + TupleReduce<TypeTransformComponentsToAddedEvents>,
@@ -83,6 +85,17 @@ impl World
     {
         let entity_uid = EntityUid::new_unique();
 
+        self.create_entity_with_uid(components, entity_uid);
+
+        entity_uid
+    }
+
+    #[cfg_attr(feature = "debug", tracing::instrument(skip_all))]
+    pub fn create_entity_with_uid<Comps>(&self, components: Comps, entity_uid: EntityUid)
+    where
+        Comps: ComponentSequence + TupleReduce<TypeTransformComponentsToAddedEvents>,
+        Comps::Out: EventSequence,
+    {
         #[allow(unused_variables)]
         if let Err(err) = self
             .data
@@ -94,14 +107,12 @@ impl World
             #[cfg(feature = "debug")]
             tracing::error!("Failed to create entity: {err}");
 
-            return entity_uid;
+            return;
         };
 
         for component_added_event_id in <Comps::Out as EventSequence>::ids().iter() {
             self.emit_event_by_id(*component_added_event_id);
         }
-
-        entity_uid
     }
 
     /// Adds a globally shared singleton value.
@@ -279,6 +290,10 @@ impl World
     /// Will panic if a internal lock cannot be acquired.
     pub fn event_loop<EventSeq: EventSequence>(&self)
     {
+        for create_static_entity in CREATE_STATIC_ENTITIES {
+            create_static_entity(self);
+        }
+
         self.emit(StartEvent);
 
         let event_seq = EventSeq::ids();
diff --git a/ecs/src/private.rs b/ecs/src/private.rs
new file mode 100644
index 0000000..56a6552
--- /dev/null
+++ b/ecs/src/private.rs
@@ -0,0 +1,2 @@
+#[doc(hidden)]
+pub use {linkme, paste};