Add Incidence struct for GraphTopology to use

src/models/graph.rs

@@ -3,7 +3,7 @@
 use typed_generational_arena::{Arena, Index};
 
 use crate::maps::EntityMap;
-use crate::traits::{GraphTopology, GraphTopologyDeletion, IncidenceCursor};
+use crate::traits::{GraphTopology, GraphTopologyDeletion, Incidence, IncidenceCursor};
 
 /// An opaque handle identifying a vertex in a [`Graph`].
 ///
@@ -23,6 +23,9 @@ pub type GraphVertexMap<T> = EntityMap<Vertex, T>;
 /// An [`EntityMap`] for [`Graph`] edges.
 pub type GraphEdgeMap<T> = EntityMap<Edge, T>;
 
+/// An [`Incidence`] for [`Graph`].
+pub type GraphIncidence = Incidence<Vertex, Edge>;
+
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 struct VertexSlot(usize);
 
@@ -66,13 +69,13 @@ pub struct GraphIncidenceCursor {
 }
 
 impl IncidenceCursor<Graph> for GraphIncidenceCursor {
-    fn next(&mut self, graph: &Graph) -> Option<(Vertex, Edge)> {
-        graph.step_incidence(&mut self.incidence).map(|(vs, e)| {
-            (
-                graph.vertices.get_idx(vs.0).unwrap(),
-                graph.normalize_edge(e),
-            )
-        })
+    fn next(&mut self, graph: &Graph) -> Option<GraphIncidence> {
+        graph
+            .step_incidence(&mut self.incidence)
+            .map(|(vs, e)| Incidence {
+                vertex: graph.vertices.get_idx(vs.0).unwrap(),
+                edge: graph.normalize_edge(e),
+            })
     }
 }
 
@@ -297,9 +300,11 @@ impl GraphTopology for Graph {
         self.raw_incidences(v).map(|(_, e)| self.normalize_edge(e))
     }
 
-    fn incidences(&self, v: Self::Vertex) -> impl Iterator<Item = (Self::Vertex, Self::Edge)> {
-        self.raw_incidences(v)
-            .map(|(vs, e)| (self.vertices.get_idx(vs.0).unwrap(), self.normalize_edge(e)))
+    fn incidences(&self, v: Self::Vertex) -> impl Iterator<Item = GraphIncidence> {
+        self.raw_incidences(v).map(|(vs, e)| Incidence {
+            vertex: self.vertices.get_idx(vs.0).unwrap(),
+            edge: self.normalize_edge(e),
+        })
     }
 
     fn incidence_cursor(&self, v: Self::Vertex) -> Self::IncidenceCursor {