Add Default trait to GraphTopologyAddition

src/traits.rs

@@ -178,7 +178,7 @@ pub trait GraphTopology {
 ///
 /// This trait provides methods for addition of vertices and edges, and capacity management in an
 /// undirected graph.
-pub trait GraphTopologyAddition: GraphTopology {
+pub trait GraphTopologyAddition: GraphTopology + Default {
     /// Returns the total number of vertices the graph can hold without reallocating.
     fn vertex_capacity(&self) -> usize;