WIP: add iterators for edges + nodes.

NOTE:
i don't like how the lifetimes worked out in the trait definitions

src/graph.rs

@@ -2,7 +2,12 @@ use crate::edge::Edge;
 use crate::node::Node;
 
 /// operations you might want to do on a graph or on nodes in a graph
-pub trait Graph<N: Node, E: Edge> {
+pub trait Graph<'g, N: Node + 'g, E: Edge + 'g> {
+    /// return the nodes of a graph
+    fn nodes(&'g self) -> impl Iterator<Item = &'g N>;
+
+    /// return the edges of a graph
+    fn edges(&'g self) -> impl Iterator<Item = &'g E>;
     // Connect two nodes, and return the edge
     // TODO: figure out a way to modify self? is that even needed?
     // same for `disconnect()`

src/test.rs

@@ -2,6 +2,7 @@ use std::collections::{HashMap, HashSet};
 
 use crate::{edge::Edge, graph::Graph, node::Node};
 
+#[derive(Clone)]
 struct SimpleEdge {
     id: usize,
     n1: usize,
@@ -12,6 +13,7 @@ impl Edge for SimpleEdge {
     type HANDLE = usize;
 }
 
+#[derive(Clone)]
 struct SimpleNode {
     id: usize,
     edges: HashSet<<SimpleEdge as Edge>::HANDLE>,
@@ -48,7 +50,15 @@ impl SimpleGraph {
     }
 }
 
-impl<'a> Graph<SimpleNode, SimpleEdge> for SimpleGraph {
+impl<'g> Graph<'g, SimpleNode, SimpleEdge> for SimpleGraph {
+    fn nodes(&'g self) -> impl Iterator<Item = &'g SimpleNode> {
+        self.nodes.values().into_iter()
+    }
+
+    fn edges(&'g self) -> impl Iterator<Item = &'g SimpleEdge> {
+        self.edges.values().into_iter()
+    }
+
     fn connect(&mut self, node_1: usize, node_2: usize) -> usize {
         let id = self.edges.len();