Allow setting value of a node without touching its connections.

src/lib.rs

@@ -51,6 +51,16 @@ impl<NodeValueT: NodeValue> Graph<NodeValueT> {
         Ok(new_node_key)
     }
 
+    /// Replace the value of `key` with value `value`.
+    /// `key` must already exist in the graph, and no connections will be modified.
+    pub fn replace_value_of(&mut self, key: &Key, value: NodeValueT) -> Result<(), GraphError> {
+        if let Some(node) = self.nodes.get_mut(*key) {
+            node.set_value(value);
+            return Ok(());
+        }
+        return Err(GraphError::from_msg("Can't set value of invalid key."));
+    }
+
     /// Get the value of key `key` if the key is valid.
     pub fn value_of(&self, key: &Key) -> Result<NodeValueT, GraphError> {
         if key >= &self.nodes.len() {

src/node.rs

@@ -46,4 +46,8 @@ impl<NodeValueT: NodeValue> Node<NodeValueT> {
     pub fn value(&self) -> NodeValueT {
         self.value.clone()
     }
+
+    pub fn set_value(&mut self, value: NodeValueT) {
+        self.value = value;
+    }
 }