1 files changed, 96 insertions, 18 deletions

diff --git a/ecs/src/pair.rs b/ecs/src/pair.rs
index 85be9f6..985a2b3 100644
--- a/ecs/src/pair.rs
+++ b/ecs/src/pair.rs
@@ -19,8 +19,91 @@ use crate::query::{
     TermsBuilderInterface,
 };
 use crate::uid::{PairParams as UidPairParams, Uid, With as WithUid};
+use crate::util::impl_multiple;
 use crate::{Component, EntityComponentRef, World};
 
+/// Pair builder.
+#[derive(Debug)]
+pub struct Builder<Relation, Target>
+{
+    relation: Relation,
+    target: Target,
+}
+
+impl<Relation, Target> Builder<Relation, Target>
+{
+    pub fn relation<NewRelation: Component>(self) -> Builder<Uid, Target>
+    {
+        Builder {
+            relation: NewRelation::id(),
+            target: self.target,
+        }
+    }
+
+    pub fn relation_id(self, id: Uid) -> Builder<Uid, Target>
+    {
+        Builder { relation: id, target: self.target }
+    }
+
+    pub fn target<NewTarget: Component>(self) -> Builder<Relation, Uid>
+    {
+        Builder {
+            relation: self.relation,
+            target: NewTarget::id(),
+        }
+    }
+
+    pub fn target_id(self, id: Uid) -> Builder<Relation, Uid>
+    {
+        Builder { relation: self.relation, target: id }
+    }
+}
+
+impl_multiple!(
+    Builder,
+    (impl<Target> _<Uid, Target>, impl<Target> _<(), Target>)
+    (ty_param_1, ty_param_2) => {
+        pub fn target_as_data<NewTarget: Component>(
+            self,
+            data: NewTarget,
+        ) -> Builder<$ty_param_1, NewTarget>
+        {
+            Builder {
+                relation: self.relation,
+                target: data,
+            }
+        }
+    }
+);
+
+impl_multiple!(
+    Builder,
+    (
+        impl _<Uid, Uid>,
+        impl<Relation: Component> _<Relation, Uid>,
+        impl<Target: Component> _<Uid, Target>,
+        impl<Relation: Component, Target: Component> _<Relation, Target>
+    )
+    (ty_param_1, ty_param_2) => {
+        #[must_use]
+        pub fn build(self) -> Pair<$ty_param_1, $ty_param_2>
+        {
+            Pair {
+                relation: self.relation,
+                target: self.target
+            }
+        }
+    }
+);
+
+impl Default for Builder<(), ()>
+{
+    fn default() -> Self
+    {
+        Self { relation: (), target: () }
+    }
+}
+
 #[derive(Debug)]
 pub struct Pair<Relation, Target>
 {
@@ -28,14 +111,17 @@ pub struct Pair<Relation, Target>
     target: Target,
 }
 
-impl Pair<Uid, Uid>
+impl Pair<(), ()>
 {
     #[must_use]
-    pub fn new<Relation: Component>(target: Uid) -> Self
+    pub fn builder() -> Builder<(), ()>
     {
-        Self { relation: Relation::id(), target }
+        Builder { relation: (), target: () }
     }
+}
 
+impl Pair<Uid, Uid>
+{
     #[must_use]
     pub fn id(&self) -> Uid
     {
@@ -46,20 +132,6 @@ impl Pair<Uid, Uid>
     }
 }
 
-impl<Target> Pair<Uid, Target>
-where
-    Target: Component,
-{
-    /// Returns a new pair that contains the target component as data.
-    pub fn new_with_comp_target<Relation: Component>(target_component: Target) -> Self
-    {
-        Self {
-            relation: Relation::uid(),
-            target: target_component,
-        }
-    }
-}
-
 impl IntoComponentParts for Pair<Uid, Uid>
 {
     fn into_parts(self) -> ComponentParts
@@ -358,7 +430,13 @@ impl<'a, Relation: Component> MultipleWithWildcard<'a, Relation, Wildcard>
             world: self.world,
             component_ref: self
                 .entity_handle
-                .get_matching_components(Pair::new::<Relation>(target_id).id())
+                .get_matching_components(
+                    Pair::builder()
+                        .relation::<Relation>()
+                        .target_id(target_id)
+                        .build()
+                        .id(),
+                )
                 .next()?,
             _pd: PhantomData,
         })