Add From and FromGraph implementations for Graph and AppendGraph

src/models.rs

@@ -1,5 +1,8 @@
 //! Concrete graph topology models.
 
+use crate::maps::ElementMap;
+use crate::traits::{GraphTopology, GraphTopologyAddition};
+
 pub mod append_graph;
 pub mod frozen_graph;
 pub mod graph;
@@ -11,3 +14,35 @@ pub use frozen_graph::{
     FrozenGraph, FrozenGraphEdgeMap, FrozenGraphIncidence, FrozenGraphVertexMap,
 };
 pub use graph::{Graph, GraphEdgeMap, GraphIncidence, GraphVertexMap};
+
+/// Builds a new graph isomorphic to `source`.
+///
+/// The resulting graph type `G` must implement [`GraphTopologyAddition`] which is used to add
+/// vertices and edges. `on_edge` is called for each edge in `source` together with the
+/// corresponding new edge of the new graph, which callers can use to construct an edge mapping.
+///
+/// Used by the [`GraphTopologyAddition`] models' `From<&H>` and [`FromGraph`] implementations.
+///
+/// [`FromGraph`]: crate::traits::FromGraph
+pub(crate) fn build_from_topology<G: GraphTopologyAddition, H: GraphTopology>(
+    source: &H,
+    vertex_default: G::Vertex,
+    mut on_edge: impl FnMut(H::Edge, G::Edge),
+) -> (G, ElementMap<H::Vertex, G::Vertex>) {
+    let mut result = G::default();
+    result.reserve_vertices(source.vertex_count());
+    result.reserve_edges(source.edge_count());
+
+    let mut vertex_map = source.vertex_map(vertex_default);
+    for v in source.vertices() {
+        vertex_map[v] = result.add_vertex();
+    }
+
+    for e in source.edges() {
+        let (u, v) = source.incident_vertices(e);
+        let new_edge = result.add_edge(vertex_map[u], vertex_map[v]);
+        on_edge(e, new_edge);
+    }
+
+    (result, vertex_map)
+}