feat(ecs): add support for entities without components

1 files changed, 10 insertions, 12 deletions

diff --git a/ecs/src/archetype.rs b/ecs/src/archetype.rs
index d2ee36a..354d206 100644
--- a/ecs/src/archetype.rs
+++ b/ecs/src/archetype.rs
@@ -4,7 +4,6 @@ use crate::component::{
     IsOptional as ComponentIsOptional,
     Metadata as ComponentMetadata,
 };
-use crate::uid::Uid;
 
 /// Archetype ID.
 #[derive(Debug, Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]
@@ -19,10 +18,9 @@ impl Id
         components_metadata: &impl AsRef<[ComponentMetadata]>,
     ) -> Self
     {
-        debug_assert!(
-            components_metadata.as_ref().len() > 0,
-            "Cannot create a archetype ID from a empty component metadata list"
-        );
+        if components_metadata.as_ref().len() == 0 {
+            return Self { hash: 0 };
+        }
 
         debug_assert!(
             components_metadata
@@ -31,7 +29,7 @@ impl Id
             "Cannot create archetype ID from a unsorted component metadata list"
         );
 
-        Self::new(
+        let component_ids =
             components_metadata
                 .as_ref()
                 .iter()
@@ -41,13 +39,8 @@ impl Id
                     }
 
                     Some(component_metadata.id)
-                }),
-        )
-    }
+                });
 
-    /// Returns the ID of a archetype with the given components.
-    fn new(component_ids: impl IntoIterator<Item = Uid>) -> Self
-    {
         let mut hasher = DefaultHasher::new();
 
         for component_id in component_ids {
@@ -56,6 +49,11 @@ impl Id
 
         let hash = hasher.finish();
 
+        assert_ne!(
+            hash, 0,
+            "Archetype ID 0 is reserved for a archetype with zero components"
+        );
+
         Self { hash }
     }
 }