Refactor ElementMap, removing its copy-on-write feature

README.md

@@ -7,7 +7,7 @@ This crate provides data structures to model graphs and to perform algorithms on
 Currently supported are:
 
 * Undirected graph types `Graph`, `AppendGraph`, and `FrozenGraph`, built on a flat, index-based adjacency list,
-* Maps to freely associate custom data with vertices and edges, 
+* `ElementMap` to freely associate custom data with vertices and edges, 
 * Connectivity and pathing algorithms: Dijkstra's algorithm, DFS, and BFS in different variants,
 * Exposed traits to implement custom graph data structures or algorithms.
 
@@ -22,14 +22,14 @@ use grapherity::models::Graph;
 use grapherity::algorithms;
 
 let mut graph = Graph::new();
-// Creates a map for edge weights with a default weight.
-let mut weights = graph.edge_map(1);
 // Adds three vertices and two edges.
 let v1 = graph.add_vertex();
 let v2 = graph.add_vertex();
 let v3 = graph.add_vertex();
 graph.add_edge(v1, v2);
 let e = graph.add_edge(v2, v3);
+// Creates a map for edge weights with a default weight, after creating the edge.
+let mut weights = graph.edge_map(1);
 // Sets a non-default weight for the second edge.
 weights[e] = 5;