1 files changed, 78 insertions, 5 deletions

diff --git a/ecs/src/pair.rs b/ecs/src/pair.rs
index 600c6e4..8bef70a 100644
--- a/ecs/src/pair.rs
+++ b/ecs/src/pair.rs
@@ -18,7 +18,7 @@ use crate::query::{
     TermsBuilder as QueryTermsBuilder,
     TermsBuilderInterface,
 };
-use crate::uid::{PairParams as UidPairParams, Uid, With as WithUid};
+use crate::uid::{Kind as UidKind, PairParams as UidPairParams, Uid, With as WithUid};
 use crate::util::impl_multiple;
 use crate::{Component, EntityComponentRef, World};
 
@@ -301,8 +301,8 @@ where
     fn uid() -> Uid
     {
         Uid::new_pair(&UidPairParams {
-            relation: Relation::uid(),
-            target: Target::uid(),
+            relation: Relation::id(),
+            target: Target::id(),
         })
     }
 }
@@ -314,7 +314,7 @@ where
     fn uid() -> Uid
     {
         Uid::new_pair(&UidPairParams {
-            relation: Relation::uid(),
+            relation: Relation::id(),
             target: Wildcard::uid(),
         })
     }
@@ -354,8 +354,51 @@ pub struct WithWildcard<'world, Relation, Target>
     _pd: PhantomData<(Relation, Target)>,
 }
 
-impl<Relation, Target> WithWildcard<'_, Relation, Target>
+impl<'world, Relation, Target> WithWildcard<'world, Relation, Target>
 {
+    /// Returns a new `WithWildcard`.
+    ///
+    /// # Panics
+    /// This function will panic if:
+    /// - The given component's ID is not a pair ID.
+    /// - `Relation::uid()` is not wildcard and does not equal to the relation of the
+    ///   given component's ID
+    /// - `Target::uid()` is not wildcard and does not equal to the target of the given
+    ///   component's ID
+    /// - Both `Relation::uid()` and `Target::uid()` are wildcards
+    /// - Neither `Relation::uid()` or `Target::uid()` are wildcards
+    pub fn new(world: &'world World, component_ref: EntityComponentRef<'world>) -> Self
+    where
+        Relation: ComponentOrWildcard,
+        Target: ComponentOrWildcard,
+    {
+        let component_id = component_ref.id();
+
+        assert!(component_id.kind() == UidKind::Pair);
+
+        assert!(
+            Relation::uid() == Wildcard::uid()
+                || component_id.relation_component() == Relation::uid()
+        );
+
+        assert!(
+            Target::uid() == Wildcard::uid()
+                || component_id.target_component() == Target::uid()
+        );
+
+        assert!(Relation::uid() == Wildcard::uid() || Target::uid() == Wildcard::uid());
+
+        assert!(
+            !(Relation::uid() == Wildcard::uid() && Target::uid() == Wildcard::uid())
+        );
+
+        WithWildcard {
+            world,
+            component_ref,
+            _pd: PhantomData,
+        }
+    }
+
     /// Returns the [`Uid`] of the pair.
     #[must_use]
     pub fn id(&self) -> Uid
@@ -585,3 +628,33 @@ impl Wildcard
         Uid::wildcard()
     }
 }
+
+pub trait ComponentOrWildcard: sealed::Sealed
+{
+    fn uid() -> Uid;
+}
+
+impl<ComponentT: Component> ComponentOrWildcard for ComponentT
+{
+    fn uid() -> Uid
+    {
+        ComponentT::id()
+    }
+}
+
+impl<ComponentT: Component> sealed::Sealed for ComponentT {}
+
+impl ComponentOrWildcard for Wildcard
+{
+    fn uid() -> Uid
+    {
+        Wildcard::uid()
+    }
+}
+
+impl sealed::Sealed for Wildcard {}
+
+mod sealed
+{
+    pub trait Sealed {}
+}