refactor(ecs): create archetype lookup entries on-the-go

1 files changed, 50 insertions, 0 deletions

diff --git a/ecs/src/util.rs b/ecs/src/util.rs
index f4f8632..5ec21c7 100644
--- a/ecs/src/util.rs
+++ b/ecs/src/util.rs
@@ -1,3 +1,6 @@
+use std::cell::Ref;
+use std::ops::{Deref, DerefMut};
+
 pub trait Sortable
 {
     type Item;
@@ -46,3 +49,50 @@ impl<Item> Sortable for Vec<Item>
         self.sort_by_key(func)
     }
 }
+
+#[derive(Debug)]
+pub struct RefCellRefMap<'a, Value: 'a, MappedValue: 'a>
+{
+    mapped_value: MappedValue,
+    _refcell_ref: Ref<'a, Value>,
+}
+
+impl<'a, Value: 'a, MappedValue: 'a> RefCellRefMap<'a, Value, MappedValue>
+{
+    pub fn new(
+        refcell_ref: Ref<'a, Value>,
+        map_fn: impl Fn(&'a Value) -> MappedValue,
+    ) -> Self
+    {
+        // Convert the lifetime to 'static. This is necessary to make the compiler not
+        // complain about refcell_ref being moved
+        //
+        // SAFETY: This is fine since we pass it to map_fn with the original lifetime 'a
+        let val_ref = unsafe { &*(&*refcell_ref as *const Value) };
+
+        let mapped_value = map_fn(val_ref);
+
+        Self {
+            mapped_value,
+            _refcell_ref: refcell_ref,
+        }
+    }
+}
+
+impl<'a, Value: 'a, MappedValue: 'a> Deref for RefCellRefMap<'a, Value, MappedValue>
+{
+    type Target = MappedValue;
+
+    fn deref(&self) -> &Self::Target
+    {
+        &self.mapped_value
+    }
+}
+
+impl<'a, Value: 'a, MappedValue: 'a> DerefMut for RefCellRefMap<'a, Value, MappedValue>
+{
+    fn deref_mut(&mut self) -> &mut Self::Target
+    {
+        &mut self.mapped_value
+    }
+}