1 files changed, 7 insertions, 7 deletions
diff --git a/graph/src/lib.rs b/graph/src/lib.rs
index 2d23af3..d4f6d7c 100644
--- a/graph/src/lib.rs
+++ b/graph/src/lib.rs
@@ -233,6 +233,12 @@ pub trait LabelGraph<T: GraphLabel>: Graph {
         Self: 'a,
         T: 'a;
 
+    /// A type that iterates over labels of an edge.
+    type EdgeLabelIter<'a>: Iterator<Item = T> + 'a
+    where
+        Self: 'a,
+        T: 'a;
+
     #[inline]
     /// Return the label of a vertex or an error if the node is
     /// invalid.
@@ -247,15 +253,9 @@ pub trait LabelGraph<T: GraphLabel>: Graph {
         }
     }
 
-    #[inline]
     /// Return the label of an edge or an error if some node is
     /// invalid.
-    ///
-    /// The default implementation always returns an empty vector for
-    /// valid nodes.
-    fn edge_label(&self, source: usize, target: usize) -> Result<Vec<T>, Error> {
-        self.has_edge(source, target).map(|_| Vec::new())
-    }
+    fn edge_label(&self, source: usize, target: usize) -> Result<Self::EdgeLabelIter<'_>, Error>;
 
     /// Return an iterator of edges out of a node, whose associated
     /// label is as given.